I could not find any clear lences, so I had to make them my self. They are casted from epoxi, pollished and then coated with PMMA. The mould can only do 10 - 20 pcs before it has to be replaced and it cost fortune in silicon to make and that is a huge part of the price.
The epoxi is an extra UV stabile grade and the PMMA coating give an extra UV protecion. Still I do not know how long they will last in a varmer climat. The Swedish sun is too weak for a test. The only guarrantee I can give is that I will replace them if you are not happy with the performance.
I sell them for EUR 20 /pcs, (EUR 76 /set) free shipping or USD 29/pcs, (USD 110/set). This is a pure hobby and I do not make them to get rich and you only pay after you have approved them.
It takes 48 hour to make one, so expect a delivery time of a few weeks.