first you should decide whether you want it to be a "push" style slave (mounted to the bell housing or block) or a "pull" style slave mounted to the transmission. Most go with the push style. I purchased one from Paula and Enzo at Finishline
www.cobraacessories.com and it sells for @ 150 and it comes with the mounting plate and hardware. You'll likely need to purchase a clutch fork as well. My slave from finishline worked beautifully, I had to weld the flange to the block and it was perfectly compatible with my 7/8 master cylinder. I remember buying a 3/4 bore MC as a back up but I don't think I had any problems with the 7/8 bore. I had perfect throw and easy pedal actuation.