Any way to still use the SD legacy receiver or if not, then any way to use the old antenna with a supported receiver?

YES-D*Tv is phasing out the SD Channels - They are no longer supporting SD receivers and the current programing change is causing your issue. 

They Should offer you a Upgrade to HD at reduced cost or Free --And the GENIE Will Not work on your current dish .

SO if you choose NOT to upgrade to resume Service --then you  should look at another provider.

The current dish has been in a stable mount for 20 years, so I am not happy about having to switch.  Since Directv has not been helpful in providing instruction, can you please point out what antenna dishes would be similar to my original in shape and size and mount?  Thank you.

And just to make doubly sure, is there really no way to continue with the SD receiver or its antenna?  (hoping that even though it is not supported, they would still have the technology running to continue it)

Can you please recommend a provider who would work with our existing legacy setup?

With your current Setup --You can live with it until it goes total dark--You need a NEW Slim line DISH --like this 

DIRECTV SL3 SL5 Slim Line Satellite Dish with Stub Mount (SLSPF-LP) (solidsignal.com)

and New LNB -(SWM) LNB -to continue your full service.  The old 18" will no longer work for full service --As they are removing SD channels from the 101 and replace them HD channels 

There is NO other Provider for your current setup 

they are offering free hd service and free boxes to switch,

goldw1800, or anyone else:

Is there anything at all I can do with my existing dish/antenna?  Is there some sort of free satellite or other television signal that I can receive with it? (before I take it off the roof for good)

Am I the only one who has written in regarding this switch?  I couldn't find any other posts, but I'm having a hard time believing that there wouldn't be others inconvenienced by the switch.

Thank you.

wheres the inconvenience? you get free equipment, free programming free dish swap same price monthly you are paying now. the dish on your roof will be useless when the satellite stops transmitting SD there is no free satellite the dish is a satellite receiver not a TV antenna. if you switch to dish network they will replace the dish as well

technologies changing embrace it and the better quality.

This last post from Constructive seems to imply that Directv is still broadcasting the SD video.

Does anyone know how long that will continue?  Is it that they are just unwilling to activate the new access card they sent to use with my old receiver?  Customer service has not wanted to try it, but Directv was the one that sent it.  Again, I am hoping to keep the current setup so I am hoping to hear from others who have successfully kept SD going with Directv.  Thank you.

@Juniper 

Could you all please take a look at this listing and let me know if this is what I need for my Genie?

https://www.ebay.com/itm/DIRECTV-DISH-SLIMLINE-KAKU-SATELLITE-DTV-ANTENNA/353228650406

Directv hasn't been helpful with this and they are leaving it to me to figure out, so I appreciate your help!

Does that listing look like it comes with everything I would need?  I couldn't tell if it included the antenna  Thank you.

They will still work until they finish shutting down the MPEG2 channels unless your area is already shut down.

With that in mind, can you please show me which dish I should get if I want to be assured of service for many years to come?  This has been a bad experience already and I am trying to avoid it again.

Goldw1800 listed a dish that looks like the one I found on eBay, so I'm hoping you can provide exact model numbers of what will get me up and running for a long time.  Thank you.

Here is one that seems to be closer to the one that Goldw1800 pointed out:

https://www.ebay.com/itm/DIRECT-TV-DIRECTV-DTV-SLIMLINE-kaku-SATELLITE-DISH-Antenna-SWM3-SWiM-3-SL3s/151418636862

Is that the correct one for my Genie receiver?  It says "This kit comes with a SL3-SWM LNB but is capable of holding a SL5 LNB or a SL3 LNB to receive 101, 110, 119 degree satellites programming"

Is the SL3-SWM OKay for what I need?

Thanks again.

On ebay --the same dish --

DIRECTV AT&T KaKu Slimline HD SATELLITE DISH Antenna NEW !!! ORIGINAL !!! | eBay

It's not really a DIY project --Call and ask for the MPEG 2 Upgrade and they will install everything 

We don't know what DTV plans for SD, some say DTV will continue some SD channels on the 101 sat but it will be in MPEG4 so no MPEG2 SD receiver will work and the round dish can receive it, but in the long run SD is dead.

Why would you buy a dish from eBay when you get it for free from DirectTV? Why are you so against a new dish which by the way uses the same mount and pole and the dish is just slipped on to the existing mount and arm and then aligned