For those that might need it, here is the stock recovery from the 2.23 RUU. If anyone is interested, I could also add to this post exactly how I get the recovery. It took me about 2 hours to get all the info together that I needed in order to pull it off.
Steps to extract stock recovery:
1. Flash stock RUU.
2. Boot into TWRP. Don't flash TWRP to phone, but boot into it running on computer. Do this by using the command "fastboot boot recovery.img". Same steps as flashing a new recovery, but in this case you just boot the phone into this version of recovery. You can use the instructions at the link below, just replace flash with boot.
3. Root phone by installing SuperSU. Flash the SuperSU.zip from your booted recovery.
4. Reboot phone and update SuperSU from the play store.
5. Connect phone to computer and use ADB to copy recovery partition to img file on phone. I used the guide at this page:
For the AT&T M8 the block you need to dump is mmcblk0p43
So the command will be this:
dd if=/dev/block/mmcblk0p43 of=/sdcard/recovery.img