Ben,
Congratulations on your purchase of Penta's. I too am looking to take the "plunge". Sounds like you might be in the UK, as I reside in the states. As was stated in a post to this thread, there are Penta's of every variety (1's, 2's & 3's) and in every quality level on eBay. If you are lucky, you can find a pair of Penta 3's for around $1,000 US and less than $200 for shipping, but you have to be both patient and persistent. I'm searching for a pair of 3's so as to avoid the whole foam rot problem that was also mentioned. I just missed a pair in great condition, but I'll eventually get a pair.
As for your 4 pin DIN connectors, you can find hundreds of them on eBay for only a couple bucks. Very reasonable! Just do a simple search and you will have them in a matter of days.
Best wishes with your new purchase.
Tom