You won't need the steel centre, since the ally pinion for the manual mags will mount directly on the shaft. No need to take the old one apart!
Draganfly used to have the aluminium pinions, deGroot BSA in the Netherlands have them listed as well (can't link directly, visit
http://www.degroot-bsa.nl/ and search for "67-0540"). Probably SRM will be able to supply one as well, you might have to drop them an email or call them.
Cheers, Markus