I wear jackets like that for work most days (one at a time).As a large chap who was larger (48 previously, now 42) Magee is a good brand, quality and fits well. They do all sorts of different tweeds so you’re not just looking at twenty shades of green. The jacket will be lined too, unlike some of the more fashion-y brands, which is important.
Some of mine have come from charity shops or ebay but as noted, you need to make sure there aren’t holes/ stains etc and you might not have time to wait for the right one to come along. There’s also the risk they might have been altered if you buy sh online – I have ones which have the same size label from the same firm but they absolutely are not the same size!
It’s a good point made earlier in the thread about material – if it’s a summer wedding, you might well be too hot with some of the more bulletproof tweeds, and some sort of linen/ cotton mix might be better. Magee do some much lighter weight lambswool too though – a good outfitter should have a choice.
Good luck 🙂