You may want to try MikesClassicCar.net. He has hard to find parts for the galaxie. Plus if I'm not mistaken, he did a short run on custom billet stainless covers for the '65-'66 brake pedal. It was a few years ago I saw this, he might be out, but I do remember they were $200 a piece.
He's not cheap by any means, so be prepared to crack the wallet open, but he seems to have garnered a good reputation on quality of parts. He has a restored '65-'66 LTD/XL/Country Squire steering wheel for $1150 if that gives you an idea of the price range of items.
Agree, MikesClassicCars has expensive prices yet the quality is high. You can count on them though. FYI I was at their site a few weeks ago (MikesClassicCars.net) and found they've revamped their website. They used to have a whole section dedicated to Ford parts but no more. You'll have to call them and see what they offer. I've talked with Eric Johnson before who's been very helpful, as I understand he's still there.
FYI, a few years back I bought their stainless 4-speed brake pedal frame-set and was very happy with the quality. Here is the same set on Ebay, from MikesClassicCars. Note that on 7-Litres the disc brake pedal does not have the center strip (it has to be removed):
This is the challenge with building 1965-66 Galaxies. Hard-to-find parts like this often aren't reproduced and if so, they can be expensive. In my case, finding a 4-speed pedal pad for a disc-brake `66 7-Litre was impossible. In the 15 years I was watching Ebay parts listings up to 2013, I only saw only one NOS pad for sale. Even then it zoomed well past $300. That was probably 10 years ago, who knows how much it would fetch today.
Hence, my options were to somehow find a real nice used one or simply switch to a non-disc pad. Given there were only 1,717 4-speed disc brake 7-Litres built and who knows how many other models with both options, it was a futile task finding a nice used one. Ended up taking a very nice 1967 automatic disc pad and trimming to fit around the 4-speed pedal. There were tricks involved, but I improvised and that's the point.
The challenge is that as most already know, in many cases (except T-bird) these rubber pads slip over the metal brake pedal and are held in place by a lip inside the back of the rubber (and metal frame if it applies). Hence, the rubber is designed specifically to fit around the pedal. The rubber on 1965-66 automatic pedals is the same, but 1967 is different, as is that for Fairlanes and Thunderbirds. So you need the pedal pad and pedal to be able to work together.
In the end, part of this comes down to what you want. Are you trying to keep your car period correct? Factory original? Or does that matter? Because if not, your options increase exponentially. If you want to stay factory/period correct, then best bet is to search Rear Counter for an NOS one and Craigslist/junkyards for used ones. Not sure if MikesClassicCars reproduced one but you can try. I've never seen it there.
Otherwise, you have to improvise. For instance, you can always buy a fairly cheap `65-66 Galaxie automatic brake pedal as a spare and see what can be done with it. Can a `67 pad be tricked out to fit on it? Can you cut the metal brake pedal and weld on another one which has a reproduction pad? If you do weld, be sure it's done well and strong because you're talking about your brake pedal here. You also have to mock up the pedal to be sure the alignment is correct with the accelerator pedal.
As they say, it's as much the journey as the destination. Just consider this part of the adventure ...