Any RD07 (1993 on) model should be OK, and the 650 Transalp calipers are also the same.
Try this is ebay; make sure you widen the search to European Union (loads more EU bits in Europe than the UK, mostly don't have the corrosion problems we see, and no tax problems). Worked well for me...
The brand new pair from Germany (261362779986) for GBP 230 incl. postage looks like good value. A used pair will probably be in the GBP 150-200 range anyway. There's a really cheap pair from Italy right now (251401152922) but postage isn't specified, and can cost a fortune from Italy, but is should be under GBP 100 all in which is a steal.
Also, if you don't know already, search this forum for "Nick Chambers", who'll do you a full rebuild with stainless pistons and also powdercoat the calipers right up to the dust seal race (the OE ones are bare alloy) for a very reasonable price. (He can also repair ones that have rotted if not too far gone, but you're probably best starting with a used pair).
If not is a big hurry I'd be tempted to grab the Italian ones and send them straight to Nick...
As Honda want around the GBP 550 mark for a new pair pretty much any of the above options are good value!
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