Have a Bushnell micro reflex that I got for my P226, is there a plate that will work for this set up?

Welcome. Sig doesn't do plates like for example Glock MOS. You don't say what 226 you have but is it one that already has a cutout for an optic? IF so then there are 3rd parties that offer conversion plates that might work I don't actually know the footprint of the optic you have (this is just one example I have used none of these...https://outerimpact.com/shop/sig-sauer-p226-pistol-red-dot-adapter-mount-m-r-a/). If its a std 226 slide and you want to use the dovetail then there are people like EGW who have again adapters that might fit your footprint (https://www.egwguns.com/catalogsearch/result/?q=226). I can vouch for EGW as a great vendor but not any of these products.

It’s an aftermarket Sig 9mm tacops slide. It’s milled for the Romeo1.

So you need to find a romeo1 to what you got adapter. I think at least one source is what I posted.

Yeah I saw the Glock #1 plate thing in my research, just wasn’t sure if it would work on my P226z I’m totally new to using a micro reflex and everything that goes with it.

Not exactly sure where you are on this. A Glock plate has nothing to do with this. You need an adapter plate from Sig romeo to whatever the heck bushnell micro is. A quick look seems to be its a doctor compatible footprint, but I wouldn't ever use one so its not something I can confirm for you.