Where to find/make Subaru 2002 Legacy body parts?

Subaru 2002 Legacy L wagon
94K miles

Car is in really good shape, except for some rust.  The rear fenders are
rusting through.  There are holes in the left rear (driver side) fender,
and a bubble-through is peeking out in the right rear (passenger side)
fender.  

I've tried several body shops, but they won't touch it, the rust is too
bad, or they can't get parts.  It's a 23-year old car, so no big
surprise that parts are no longer available.  It isn't just the outer
fenders that are needed (that have the rust holes), but also the inner
quarter panel that has the flange to which the outer fenders are
attached.  The inner quarter panel has the flange to which the outer
fender panel attaches, and the flange is always rusting away.  So, outer
fender, inner quarter panel, and on both sides.

No one I've contacted can find the replacement parts.  There are places
to find used parts (e.g., car-part.com), but anything that will fit will
be as old as my old car, and be rusted.  Don't want to replace a rusted
inner quarter panel and outer fender panel with parts already rusted.

Estimates, if the parts were available, have been $5K per side, or $10K
total (barring surprises), so usually the advice has been to not bother
with the rust repair, let this one degrade into a rust bucket, and buy
another car.  But I really like this car.  Other than the fender rust, I
can't get a used car in such great condition for $10K.

When I bought it 2 years used, it had 64K miles.  I had it inspected by
a car shop for $150 to see if it was a good buy, and it was.  Very
reliable in the 21 years that I've had it.  I did get nailed with
Subaru's screw up in the manifold gasket that had to get replaced, but
overall the car has been a good runner.  In the 21 years that I've owned
it, I've put on all of 30K miles.  I don't drive much, and much of what
I buy gets delivered, including groceries.  94K miles is low for this
boxer engine which typically is good for 300K miles.  Everything is in
superb shape except those rusting rear fenders.

But I can't get the parts!  car-part.com lists some parts at various
grades (A, B, C, X), but clicking on the pics brings up a page saying
"invalid selection", but there is nothing else on which to click to see
the part.  I can find fenders there, and fender inner panels (which I
assume are the inner quarter panels).  Besides the part cost, I'm sure
there is a shipping cost.  

Of the body shops that I've visited, most are oriented toward collision
repair, and won't touch rust repairs.  I found one independent shop that
quoted a cost for rust repair of the LH rear fender ($5400), but I think
he forgot to include the inner quarter panel.

I like this car, and owned it for 21 years of its 23-year lifespan.
Miles seems low for a car this old, so it'd be nice to keep it another
10 years, or more.  Just not sure I want to toss $10K, or more, into
making it look nice.