You can try Cathay Photo at Peninsular Plaza or Marina Square. Alternatively here are a few other options.
MS Color at Ang Mo Kio
Alanphoto at Sim Lim Square/Funan Center
For used Tamron lenses. try the Camera Workshop and the likes at Peninsular Shopping Center/Adelphi etc. Or www.clubsnap.org.
Cheers,
Bookmarks