Okay, it's not April 1, but here is what it sort of would have looked like had the mint issued any Standing Liberty Quarters in Brilliant Proof. This silver round is a mixture of the Type I and Type II & III quarters. The head of Ms. Liberty is Type I like while the rest of her is Type II like. This one is from @Mountain Man who kindly sent it to me. Here is a Type I Standing Liberty Quarter. Here is a Type II Standing Liberty Quarter.
Hooray for Hermon MacNeil, and hooray for @Mountain Man! Are there still people who believe a few SLQs were struck as proofs, or is that completely discredited at this point? In a 2012 thread here, there still seemed to be some disagreement.
I would love to have a set of these, but way too expensive in the condition I desire, These and Peace Dollars are my favorites. These shown are beautiful.
If there were any Proof Standing Liberty Quarters, they would be Matte Proofs. The PCGS Coin Facts site does not list any. Walter Breen stated that there were two Satin Finish Proofs reported. Breen sometimes had an active imagination, and in this case, he only said that they had been reported, not confirmed. I would say that none exist.
I only have a few. But, I agree with you the Standing Liberty Quarter is a beautiful coin. I was lucky enough to get a 2016W Standing Liberty Centennial Gold Coin. I was also able to get the 2016W Liberty Walking Centennial Gold Coin and the 2016W Mercury Dime Centennial Gold Coin.