For Brits they're sure confused about Lee Enfield nomenclature! http://riflemags.co.uk/lee-enfield-magazines/

Looks like they only make a 10 round mag for the No.4 or No.5 Rifles, with a half-cut version for "sporting" use.

None are historically correct for Lee Speed rifles, or even sporters based on the No.1 (aka SMLE) Rifle.