Tire sizes and where to buy

Well, in anticipation of spring, I'm gonna buy some new sneakers for the Meejit.
What's on there now is 145 RA 13 Michelins, badly weather checked and pretty
worn.  Questions:  What size are people running?  What brand?  And where on the
net can I get some info on prices?  I went to tirerack.com  but they don't
exactly seem to cater to little teeny tires!  My use will be, shall we say,
aggressive street, summer only.  Thanks in advance for any help.

Geoff Branch '74 Meejit "Yellow Peril"