Don't know if you're still looking for an answer on here, and I'm no expert by any means, but it's my understanding and experience that PVC is a sub par core to fiberglass no matter what. It is much more prone to both flex and break. Although flattening it might make the core stronger in one direction, it would also weaken it in another. If you accidentally flatted someone with a super flexy blade with only one layer on it they'd probably be unhappy.
If you're looking for an easy to get core, I'd recommend dual coring 3/8ths in fiberglass rods or golf clubs. Neither is by any means ideal but I've done both with a small bit of success. Plus if you get the fiberglass and get very into foam smithing you can break them down and make a couple javs.
Sorry if I'm too late to be much help I thought I'd proclaim my opinion to the Internet.