I believe there are a couple in the Repo. It’s mostly just well known characters like Leif and Nanna with a couple of outliers like Shiva and Trude, though.
This topic also has tons of other links for resources that you should look into. Just remember to check whether portraits are F2U (Free to use) or F2E (Free to Edit). And always be sure to give credit and reach out to the creator!
If you want the exact FE5 portraits, there aren’t any ‘direct’ ports of them for the GBA games, at least none that I know of. This is mostly because SNES portraits are, like, half as wide as GBA portraits. Characters also don’t have map mugs in Thracia, either.
You definitely could just download some FE5 portraits from the wiki and insert them into the GBA format, but that’ll take some time and the end result would be small, skinny portraits that would look strange when placed next to the GBA characters.
BTW, in case you’re wondering, the program I use for editing portraits is called Usenti. It’s really good for this sort of thing and there’s plenty of tutorials for how to use it online.