I've looked around (I know I've seen vintage looking emblems for sale that weren't 260/289...)
Restore Mustangs have some but only 260/289/302/5.0 the same goes for John's Mustang but perhaps if you call one of them they will be able to answer your question. California Mustang and Year One seem to have even less (based on their online catalogues) and NPD doesn't have their catalogue online yet. I don't have the paper versions with me.
You can always put 260 ones on and see how many people believe it until you drive off. ::
Have not found them, so I made my own 306 emblems. I carefully cut apart a 289 and a 260 emblem, and then rearranged the numbers onto a hipo back plate to get "306" The "3" was a "8" cut almost in half ( looked just like a perfect 3 ), and the "0' and "6" were from the 260 emblem. They looked nice and I used to have a pic which I can't find anymore. I gave them to a fellow VMF'r 'cause I decided to go to a 331 stroker. Soon i'll be making a set of "329" emblems for it. I chose "329" cause it sounds good ( kinda like a little bro to the 429 ), and I can use just one 289 emblem and a hipo back plate to make it.
As far as "347", you would have to mold a 4 and a 7 since neither is on the 260 or 289 emblem. "339" would be easy, or "360", or "393" if you had a 351 stroker. I should get the pic and show you how nice they looked. Maybe i'll have to make a few sets and sell them since I se this topic pop up often.
Here's a pic of the 306 emblems made a while ago which I gave away. I'll be making a set of "329" emblems soon for my stroker. I used to work with molds and reverse molds, so if I could make up a "4" and a "7" I could make "347" hi po emblems and mold them. Just have to find the time, but maybe there is a market out there. I cut and reassemble the emblems onto a hi po back plate epoxied together and then touch up the black paint. It took a while to make up the set of 306 emblems, but the next set won't take as long. I'm limited to 2, 3, 8, 9, 0, 6 for numbers right now. It is labor intensive, but I think they are different and looks cool. I'm going to tap the posts on the emblems so someone won't be able to pull them off and steal them. Right now I can make "302", "306", "329", "330", "333", "339", "360", "393", etc. with the numbers I have to work with.