I bought my last 3 sets from Ron Ayers. Best prices I could find at the time. You need to shop around and compare prices and shipping for what you want - lots of "bad economy" sales going on.
And the sizes are, er, on the sidewalls of the tires.
The "tech vault" section has some info on tires. Once you've decided on which tires you might want; check to see if the shop you're having put the tires on (assuming you're not doing it yourself) can get them for you. I found my local shop could give me as good a price as online, had them in stock, and sometimes they cut you a break on the install and balance if you bought from them. FWIW I replaced my front original Bridgestone with a Metzeler ME880 100/90-18 and I couldn't be happier with the results. I highly recommend this tire. When I replace the rear I'll go with the ME880 to match.
'05 America, 904, K&N pods, British Customs Bomber Exhaust
Steelheart- '03 Speedmaster Black/Yellow
The Hayabusa Killa
16" Shorties/140 mains/Airbox drilled
Procom CDI
"There is no cure for Celibacy. But we can treat the symptoms."