Hi Steve,
Pity Revell are dragging their feet, I've usually had good service where replacement parts are concerned, just recently I got a part from Testors in no time, and I got a replacement for a broken prop on the Ar 196 from Airfix a few years ago. You could drop them a line, open an email dialog -- chances are the business has been lost in the system, not ignored. Don't give up!
But if you need to fabricate a replacement, you can. It'll take work, but it can be done. I've used Alumilite for about three years and it's good stuff. It's neither magic nor rocket science, and there are many ways for the job to go wrong, so be prepared for plenty of reject parts.
You'd need to sacrifice one of the props as a pattern. My impression is you'd need to cast the spinner and the blades seperately, allowing for one-part molds, a LOT easier than a two-part mold -- though you could cast the prop in one go in a two-parter (base of the blades would be very fragile, it might not be worth the effort if they snapped straight away). Air bubbles are the biggest problem in home molding, as it's not usually possible to afford a vacuum chamber to de-gas the resin (nor does Alumilite's three-minute pot-life really give you time to).
The ins and outs of casting are detailed on Alumilite's website and they always include plenty of technique paperwork with their products, there's a how-to booklet that's always lots of help. Give it some thought -- if you need to enter the world of casting, it's a great skill that'll serve you in future. I use it for repetitive structures in SF scratchbuilding and it makes possible many projects which would otherwise be non-starters.
Cheers,
Mike/TB379