Hey Moose, first off, Welcome to our happy little corner of the net, and to our Club. There are TWO BIG fridge'S in the corner with anything you can think of in them...help yourself...of course only take what you can LEGALLY have. (stash)
make yourself at home on one of the big fluffy couches, kick your shoes off, put your feet up on one of the tables, yes we are allowed to do that, mom don't care....and take it easy.
oh...btw....every once in a while a food fight breaks out...so you may not want to wear nice clothes here.
Welcome!!
As for your shifter questions.....the answer to the diameter question is this....the B&M's thread size on the shifter is 10MM X 1.25 so if you are going to get a knob that has a threaded insert, that is the size you need.
as for websites....hit yahoo or google or lycos or whatever your favorite search engine is and put in SHIFT KNOB and you will have more to look at than you can shake a stick at....once you find the knob you want...then start shopping for prices.