I doubt you'll find anyone who will make them on demand. You're basically limited to whatever is available at the moment.

There's a thread on here somewhere with advice/directions for DIY replacement plastics. It's likely the best option for less popular titles, if you can't find what you want with a WTB ad or an eBay search.

Thanks! A lot of times I'm on my phone and it's so hard to hunt things down and post at the same time.

I doubt you'll get anyone publicly offering the service, since they would likely be making them without proper permission/licensing. I don't see it happening unless it's DIY.