Cartridge mount screws - stainless steel


I need longer mount screws to mount my cartridge, can i use plain steel screws or must i use stainless steel screws . I am having a hard time finding small stainless srews, 20 mm long locally.
tshulba
Thanks guys i have tried a local hobby shop and one bolt supply and they have shorter stainless but not 20mm. I may have to machine up my own out of brass once i find the proper size die to cut the threads.I found plain steel screws at Radio Shack but it looks like i can't use them.
Here is one option. 2.5mm x 20mm stainless socket head cap screw. 12.59 per pack of 50 from McMaster-Carr. Have enough to hand out to friends!

Punch in this part number:

91292A019
Is 2.5 -20mm the right size for Shelter 501 MKII?
McMaster-Carr does not have metric sizes brass screws.
Any other sources fro brass?