I buy practically everything from EBay. Just search there. The cheapest I found were in the UK. I’m in the US. You can get them for just over $300 a pair shipped. There are some places selling them for much more. I think there is a seller I saw in the US but price was more than UK. The EBay seller I used goes by Roundandblack or something close to that. Good luck 

Holy moly the Shinko tires I bought were only about $130/pair. Those tires much be amazing!

Thanks!
Next question, LOL, what width rim strip's did you get for front and rear?

Yeah for the correct size and tread pattern to closely match the original Dunlop you have to pay up. Shinkos don't offer it.

For rim strips I just bought (1) for 18" wheel and ( 1) for 19" wheel. I didn't buy the whole package from the UK. Rim strips are available multiple places just search Ebay for best price. I've also used my local cycle repair shop for generic things like tubes and strips. Bikemaster makes a lot of parts. 

Just a tip… Yamaha tubes and strips are quality name brand (ie Bridgestone) and often cheaper than anything else. 

I just ordered the Heidenau  K67's. A rear 4.00 x 18" from RevZilla - $125 with shipping, and the front 3.25 x 19" from wyldebike on eBay out of the UK for around $165 shipped with the exchange rate. A bit cheaper than Roundandblack on eBay out of the UK, and he wouldn't ship to Pennsylvania. A local dealer that sells Heidenau's made a couple calls for me and was told the 3.25 x 19" won't be available for a few months here in the US.
Thanks for the help Pedalcrazy!

That 3.25x19 Dunlop trials tread has not been available for a very long time. I would think if you found one it would be rock hard. Ok for a stationary exhibit maybe.

I found a set of Cheng-Shin trials tread 3-4 years back. Not "correct", but certainly 'period-correct' anyway. They'll go on when I get the rims laced back up. Waiting on the chromer at this point.

Interesting to learn about the Heidenaus though!