Peatol Machine Tools supply the very same Sherline spindle heads that you are looking for, I came across them when I was looking for s spindle for my machine but in the end decided to build my own as I wanted something a little bit stronger.

Check out the post on my DC spindle build, may give you a few ideas for an alternative way of doing it.... http://www.mycncuk.com/forums/showth...machine-DC-1HP