It's really not all that easy to set up a gangbang from scratch unless you've been in the lifestyle for a while and have contacts to call on.
Also you say your wife has only cheated once. I think in that case, she's unlikely to want to dive in at the deep end and go straight to a gangbang. If you really want to get somewhere, start off slowly and just encourage her to fuck men she's attracted to and see if she wants to build up to two and then three men at a time.
If you try to push her straight into a gangbang, I think you're more likely to just scare her off the whole idea.
She's very attractive so she'll have no problem finding men to fuck her but let her enjoy it at her pace.
My wife has had many many gangbangs over the years and it is very hot to watch your wife getting fucked by several men at a time but it's not something you should try to rush. It's much more important to build up her confidence by letting her fuck who she wants and showing her that you can deal with that without getting overly jealous or getting cold feet once she stosrarts playing with other men.
James