Having a bit of a clear-out in my retirement and so have a matched pair of Monacor RBT-20 ribbon tweeters for sale. These are true ribbon tweeters and probably are made by Fountek under licence for Monacor. The aluminium face plates are 127mm dia.
The cheapest online current price for these I can find is from a German seller on EBAY at £268.80 with free postage to UK. I expect you may get stung for import duty and VAT by UK Customs? Cheapest UK seller I could find was Willys Hifi at £276.56 plus p&p. However they currently do not have any in stock.
I'm asking £150.00 + postage at cost.
Datasheet can be read here:
http://www.audio-talk.co.uk/colin/pdf_m ... T-20_1.pdf
and publishers FR graph can be viewed here:
http://www.audio-talk.co.uk/colin/G105710K.pdf