The objectives from a cheap pair of 8 x 30 Kmart binoculars work well.
Surplus Shed usually have some good stuff, Thorlabs/ Edmund are also good but very expensive!!!
Reflection gratings - I always buy from Optometrics (now part of Dynasil)
https://www.dynasil.com/catalog/diff...hick-standard/
The 600 l/mm is a good starting point.
Check out our webpage:
http://www.astronomicalspectroscopy.com/instrument.html
Any questions....just ask.