Well, I'm assuming that the bike you're talking about is the one pictured in your avatar.
First thing I would suggest: Loose the seat.
I've ridden on a seat like that and they are not comfortable. Keep an eye on ebay and Craig's list for either a stock seat or a cafe seat that you like.
Second suggestion: Get some new bars.
Clubmans, drag or clip-ons can all be had for cheap. It's amazing what simply changing out the bars can do for the stance and
feelings of performance.
From there, it's really up to you as to which direction you want to go. Rearsets, knee dents, crazy paint, $1200 exhaust... (oh wait... that last one was me...
).
Make it personal. Make it yours. Ride the tires off of it.
We will be here to help with questions when you have them.
As for places to get things, just hop on Google and type in "Cafe Racer Parts" or something like that.
http://www.denniskirk.com/jsp/common/Frontpage.jsp The every present supply place.
http://www.bikebandit.com/ I like these guys, too. They give a discount to
AMA members (See my signature to JOIN!!)
www.mikesxs.com Mostly designed for the Yamaha XS 650 bikes, BUT some good parts we can use, too.
http://www.yamiya750e.com/ Good for some cool stuff you never though to replace until you saw a shiny new one.
http://www.cb750cafe.com/ Carpy's site is great with some cool stuff (He's a member here, too, and stops by from time to time).
And once you've saved up your pennies and it's time to dive into the engine:
http://www.cbrzone.com/ Prepare a bib before entering, as there will be drool if you have any enthusiasm for hopping up the power from your 35+ year old engine.
Good luck and keep us up to date. We love seeing new projects get underway - and then get completed.