You'll really struggle to find old 27" rims with 40 holes at a sensible price. They are rare and only pop up from time to time so always command a high price. If you're not too worried about going to 36 spokes front and back I think your best bet is to either look out for a pair of second hand replacements (loads on eBay) or check out some of the new wheelsets on eBay:
Bankrupt Bike Parts often has 27" wheelsets for sale, but I can't comment on the quality:
http://www.ebay.co.uk/itm/201225146467
I've got these on
her bike and they are bulletproof, but not polished:
http://www.ebay.co.uk/itm/351224116938
I've not used them yet, but they've been around for ages and I know other riders who have used these guys' wheels and said the quality is good:
http://stores.ebay.co.uk/Single-Speed-Components