Well, I've never actually tried using FL Studio before; I use a lesser known program called SynthFont. While I can't recommend an original soundfont, as I've never actually delved into making fully fleshed out original or remixed songs, I would say my personal favorite soundfonts would be the Sega Genesis soundfont, and Mario Kart DS's Title Screen soundfont. I can't remember exactly where I acquired the Sega Soundfont, but I do know that I got the Mario Kart DS soundfont directly from MKDS's ROM file itself.
(Also, many apologies for being so late, I check Pokecommunity extremely sparingly.)