Most LFS's sell them so i think that you should have some luck with finding some, which tank are you gonna keep them in? and i would highly advise that you do not get bumble bee gobies if you have tiger barbs.
16 gallon - 11 neon tetras, 6 Pygmy cories, 6 kuhli loaches and 1 male Betta
15 gallon - 1 male Betta, 3 platies, and 5 guppies
6 gallon - 1 male Betta
All planted tanks
In My Opinion a Betta deserves nothing smaller than a 5 gallon tank