Please don't say "metric", it causes much confusion. :)
The heads are probably "pre-international" sizing.
You can order heads from your local shop or hit Ebay for heads.
Here's various sizes and head types:
BA-0110-PR- Ambassador, Coated, 10"
BA-0112-PR- Ambassador, Coated, 12"
BA-0116-PR- Ambassador, Coated, 16"
BR-1120-PR- Ambassador, Coated, 20"
PS-0310-PR- Pinstripe, Clear, 10"
PS-0312-PR- Pinstripe, Clear, 12"
PS-0316-PR- Pinstripe, Clear, 16"
PS-1320-PR- Pinstripe, Clear, 20"
BE-0110-PR- Emperor, Coated, 10"
BE-0112-PR- Emperor, Coated, 12"
BE-0116-PR- Emperor, Coated, 16"
BE-0320-PR- Emperor, Coated, 20"
Yes, these are Premier heads, they will fit any pre-int kit.