Custom Canopy Makers?

I don't know about custom canopy makers, but you might be able to do it yourself after all. Not sure what the difference between the "C" and "D" variants are, but if it's just stretched or you can otherwise make a mold for it (balsa wood or something like that would probably work) Squadron has some clear plastic called "Thermaform". Heat the sheet over a candle then quickly pull it down over the mold and it forms around it. It's useful when a canopy gets cracked or something like that, and might work for what you need.

Squadron also has a line of aftermarket canopies and they might have an Academy F-18D canopy available. They are an excellent company to order from, I've ordered from them several times and highly recommend their service.

Their website is at www.squadron.com

There's also thermaform where you stick the clear sheet to a steel frame and push the master down into the heated sheet. Two different ways to thermaform. Super Sculpey is a clay that can be used as the master in that kind of heat. I'd use Super Sculpey for that not Milliput.

Thanks Guys!
Thanks Music City
Externally, the difference between the F-18D and C is the the D is twin seater, while the C is only a single seater. The D cockpit is extended rearward. The Fuselages for both are the same length, no stretching. Academy provides almost all the parts for making a 'D' (As well as parts for making almost any F-18 you wish). I maean they have the double place cockpit, and part of the spine is a separate part, so switching the conversion will be easy from that stand point. The rear cockpit is a scrathbuilder's dream: It's totally featureless, so I would have scratchbuild all the rear details, but it looks easy enough to do, and Academy does not include a true 'D' instrument panel, but scratchbuilding one of those is easy, especially if I use a Eduard F-18 interior set(probably will use two for the model.)
Thanks for the tip on squadron. They are my favorite online Hobby shop. I didn't know that they had all that available, though. I will definitely give that the Thermaform a look.
Thanks jdavid b for the tip: I forgot about Sculpey to tell you honestly. I like working with it better than Milliput.
Thanks all you guys for your help. I will give these techniques a try.