Just for a little disambiguation: we're talking about master and valet keys here. . a valet key by definition only operates the doors and ignition. . not the glove or trunk (if those are equipped with locks). People sometimes confuse non-remote with valet keys. A non-remote key will still do everything a master remote key will, it just doesn't have the fancy buttons to let you do it. . .remotely.
Before Subaru HS blanks were available, we would make them from Honda HS blades. . . just have to shave it down to the same width as the Subaru blank first, then duplicate. It can be done, sounds like your guy knows it can be done, buuuut. . .
JMA makes "shell keys" for Subaru already, so there's not really any need to. They look like this:
and they sell wholesale for about $2.50. We sell them cut for about $25. Why? Because the machine needed to cut them accurately was bloody expensive (cheapest one is about $8,000 right now--they've come down a lot. . .and we didn't buy the cheapest one when we bought the one we have).
A shell key is one that has no transponder loaded in it (that little red thing holds the chip and slides into the rest of the key), so you can use them to either build a keyblade/chip combo that does not exist in the aftermarket, or to repair a customer's broken key (cut out the chip and transplant it to the new key shell, no programming required). We do superglue the little red insert in once we've loaded a chip into it and tested the blade, otherwise it might fall out and we'd have a rather unhappy customer.
There are two very big locksmith distributors right there in or near SoCal that I trade with occasionally. One is American Key Supply, the other is National Auto Lock. I don't know if either has a retail division but I'm sure they could hook you up with someone local who has the blank, or perhaps point your guy in their direction. They will sell onesy-twoseys on shells, in case your guy doesn't want to stock any more Subaru keys than the one sale you're bringing. If you tell me where you're at, I can probably suggest somebody without all the cold calling.
In your situation and doing it remotely, the only thing I could make would be a shell key (which would work the same as a master) with no chip in it. I can furnish the chip if you'd like to maybe have it programmed in someday. That can be done at any Subaru dealer or a well-equipped auto locksmith. There won't be much functional difference between the key I make and a "valet" key from Subaru. . .mine will open the glove box, theirs won't.
Just for the record, the chips themselves are pretty much waterproof. . . so it'll live through anything you will.
So there ya go. . . what I can offer isn't really that special in the grand scheme of things, just sounds like you haven't been talking to the right folks over there. For every 10 locksmiths, you might find 1 that really knows cars. . . factor in a small brand like Subaru and that figure probably drops to about 1 in 20.