Alan, do you mean 13 x 8 or 15 x 9 ? i was unaware they made 15 x 8's but happy to be corrected. I though they only made 13 x 6, 13 x 8, 15 x 6, 15 x 9.
If you draw a blank, I can make you one like this https://flic.kr/p/NyRhnL It's designed for a Minno shuttle and comes flat packed so can be posted. It's £249 + Post. You have to strap each tyre down separately with 1 inch straps from screwfix http://www.screwfix.com/p/ratchet-tie-down-straps-with-j-hook-4-8m-x-31mm-4-pack/37983 it doesn't have the standard "bar" wheel holding system because that doesn't work with 6 and 8 inch wheels - the 6's hop out because they are not held in.
I can change the glass for you - it's £130 fitted in your existing screen using new rubbers. This is unheated glass and I can normally turn this around in about a week. I'm located near Stansted airport (15 mins) i can also get windscreen surrounds bead blasted and powder coated for additional charge. PM me and we can go from there.
I have a full set of 6" anthracite wheels with CR500 tyres. Tread on the tyre tread varies from 2mm to 4mm. Pictures here : https://www.flickr.com/photos/124950518@N08/shares/Y85Ney Located 15 mins from Stansted Airport Can post at cost. £500
If you send me a link to the ones they are on the caterham website that will be fine. what are they 2" or 3", aero or road ? I'll have them if you let me know what they are.