Lewm,
If you want a MK3, I've been searching for them long enough to be able to direct you to one.
Before you say yes, expect to pay minimum $5000.00 and a high of $10,000.00. A MK 3 at Audiogon a while back was listed $10K, it was supposed to be "new" in box. Occasionally they are at Ebay, but I've seen half a dozen at Ebay with the same tired stolen images and always offered on a hijacked or new account with no feedback.
All MK3 I've been able to find are outside the USA. That does not mean there are none here, but rather I don't know where any are for sale. Maybe Steve Dobbins has one? You might check with him.
If outside the USA, remember you must wire transfer money first and pay shipping. My MK3 came from France and when it arrived at DFW Airport Customs held it.
I drove out, wasted half a day and finally got it out of hock. It was packed pitifully, but thankfully undamaged. It was shipped Schenker Air Cargo, that's probably what saved it. Packed the way it was, if it had been UPS I would have had a pile of junk.
I'm not trying to discourage you, just stating the facts.