I'd also be careful in general about fitting aftermarket MB body
parts.   If you can at least see it, and not buy it blind, that's
helpful.   There are many cheap body parts out there that are not made
precisely and fitting them and making them work eats up as much time
in labor cost as you save in part cost.

I recently had some body work done on my car by a guy who does top
quality work and has been in the business 40 years.   We went through
the options and elected to use a combination of salvage parts and
genuine MB parts.

For the MB bumper, you could try Rusty.  He's gotten me genuine MB OEM
parts at reasonable prices.   You can google for Rusty Mercedes
parts.