I couldn't believe Midway doesn't have one especially for the 887 but I just looked. Is your receiver drilled and tapped already? Can you measure your hole pattern and match up a universal?
A machine shop won't be cheap on a custom piece like that. I would measure the hole pattern and match it up with a universal on Midway. Cost you less than $20 I bet.
weaver has a 3 hole for remington, it fits the 510 model or something like that it also fits the 887, i know i bought one but can't remember the exact number, you can call remington and ask what model fits it and match it with another remington. bass pro had them
I would go with universal. I run a machine shop and its $65 per hour for just about anything. I have room to move some but most shops are not willing to do work on guns just incase something happens to it.