Just do it!!
There is an enormous difference between fantasy and reality which is very apparent at times on this forum. Unless we were actually thinking of buying a wedding dress and renewing our vows and all dressed for the occasion there is no way a retail store would entertain the idea of a couple visiting the store and a male just trying on what are usually very expensive gowns. That is an area of male fantasy only unfortunately. However, there are charity shops around that often have wedding dresses donated as well as other “exciting” female outfits and it is quite possible to measure someone and even try on outfits in such places. Often they are staffed by more senior members of the community who have probably “:seen it all” at various times. When I visit such places with my wife, she often holds up skirts and dresses and suggests I might like them and we do buy the occasional item to add to this maid’s wardrobe. A few years back we used to see more lingerie and general female underwear available in charity shops and it was a great place (although somewhat embarrassing) to acquire some more traditional foundation garments such as girdles and corselettes and the odd slip or petticoat. These days it seems that most of them do not stock underwear…seems to be a hangover from covid times, perhaps attitudes towards personal hygiene?
Anyway,. If anyone knows of a bridal store where the staff encourage men in drab to enter and try on a gown or two, do share the info, it would be an enlightened store indeed!
I don’t know any physical retail stores, but there are amazing sellers on Etsy that make incredible garments including sissy wedding dresses. I have a few handmade bespoke sissy uniforms that are jaw droppingly beautiful, and the experience of buying and liaising with the seamstress while being made was wonderful. So there’s nothing to stop sissies having an incredible wedding dress!