I bought my cufflinks on Etsy. They’re a vintage mother-of-pearl pair that cost me $5. You could easily go and find new ones, but vintage works just as well and there’s plenty of deals to be had. Same goes for studs. It’s worth noting that I didn’t buy any studs since I bought a tuxedo shirt that has a hidden placket, so the buttons aren’t visible and there’s no need for studs.
For a bowtie, I bought a skinnier black one from Thomas Pink. The Tie Bar has decent (and cheap) bowties as well. Really, it just depends on your budget and what you want to spend.
Kent Wang has all the wedding accessories you might need, if you’re looking to buy this stuff new.
As for opera pumps, I have no idea where you could affordably buy a pair beyond getting lucky on eBay.