I was wondering if there were any 5/6 spd manual transmissions that could bolt to my 350?

 

TKO 5 or 6 speed will work. You will have to modify you driveline and use a stick bell housing but you can buy a whole complete kit from.

http://www.classicchevy5speed.com/TKO-Details.aspx

These transmissions are sold by several different suppliers. I am install one in my 48 Olds behind a 455

 

The TKOs generally wont fit the A body tunnel.
Check out the Richmond 6 speed. Uses your old driveshaft too.