Where to find black tie formal wear

I'll start by saying I hate using AGABs but in this case it's relevant as my predicament pertains to how clothing fits my current body.

I'm 33NB, AFAB but very very heavily masc leaning (think pre-everything transman appearance but identifies as NB). I'll be attending a black tie event for a work thing, attendance is mandatory and I want to go. However, where the f do I buy gender neutral formal wear in the UK? I want to wear a black suit but can't find anything that's not men's wear.

I looked on Androgynous Fox, GFW Clothing, and Peau de Loup, but I can't find a plain black, long sleeved shirt. They all either have short sleeves, a weird fabric, or a print. Trousers are a nightmare because any mens trousers that fit my hips and arse are far too baggy and long on my legs.

I can't buy mens clothes because I'm 5ft 1in and have a chest and hips, so anything that fits me horizontally doesn't fit me vertically and is baggy in the middle. I do bind, but my chest is too big to disappear entirely so I wear slightly baggy tshirts day-to-day to hide what remains.

Can anyone recommend somewhere that does gender neutral fitting plain black shirts and/or trousers. Or can anyone suggest a different solution?