You can try calling Derek Leland Tisinger (661-747-5796) he is a solid source of many new/used parts for FL350's and probably has everything you need.
He also sells an aftermarket intake that allows you to mount a K&N style air filter. In place of the OEM airbox.
There is also
https://oddballorv.com/ for some new aftermarket parts that may help you, these can be pricy though.
Oddball also sells the same aftermarket intake as Derek.
And of course Ebay...
If you get an aftermarket carb don't get a Chinese knockoff. They are almost always more trouble than they are worth.
38mm carb works and is definitely an upgrade but can be a pain to stretch over (and lends to the possibility of ripping) the original intake boot if you have one.
A 35mm PWK Air Striker carb is a good option also.