Looks like part "34" (Magazine Retainer & Ejector, Rear) from Numrich Arms schematic of a Savage Model 23A sporter. In looking at the 23AA, that model is later and the magazine retainer parts are different.
I don't know of another good source for odd-ball parts beyone these guys. Perhaps, you might investigate seeing if you can find a REALLY GOOD WELDER (small, intricate, delicate parts ... not my kind of Farmer welding).
They are out there. I had one (dead now), Dick Nickle out in Washington State. I had a British 22LR Vickers and the piece that cocks the firing pin had broken, He welded that up over 25 years ago and it still shoots today.
I would NOT give up. Since this is a family rifle, you might even keep your eyes open on the usual gun auctions for a #23A (not 23AA). If you can buy it cheap enough ... you have a ton of parts and keep a family heirloom in operating condition.
I'm a Savage Sporter nut, inexpensive rifles that just feel good when you throw them up to your shoulder. Nice shooters too. That whole "23 series", (and 19 and 19-H as well) ... the 23A and 23AA in .22LR, the 23B in .25WCF, the 23C in 32WCF and the 23D in .22 Hornet are some of my favorites.