why the temples are unavailable with length 150 mm?

[mens glasses]

I need 150 mm plastic temple length for metal frame- I try many websites to look for this kind of eyeglass frame, but unlucky, their customer service always tell me that it is unavailable with 150 mm. Why?? i need a pair of metal eyeglass frame with the plastic legs (150 mm), and also, the color of frame must be gunmetal or silver. thanks for any help.