I'm very new to hexbear and mostly lurk, so I'm not sure if I'm allowed to recommend an online store (I also don't know where you're located, the store I have in mind only ships within Canada and the US), but anyway there's a worker owned sex store cooperative in Toronto that has a great online store.

All of their gender gear descriptions are super gender neutral, I just checked to make sure and there's even a line about packers being for everyone who wants one, in their basic packer information.

I try to never shop for sex stuff anywhere else, unless it's something I legitimately can't get through this store.

If I'm allowed I'll totally give you the name, or you can DM me about it.

Depending on what exactly you want in a prosthetic (just a flaccid bulge? Pack and play? STP?) there are also people who make stuff themselves that you can sometimes find at queer markets or online places where artisans can sell stuff. If you're crafty and just want a flaccid bulge, I could send you the pattern for a crochet packer.