ᐅ Flush-mounted or plasterable access panels for chimney pipes

Hello everyone,

We are currently renovating our bathroom. Now we want to replace the inspection openings for the chimney pipes.
It would be ideal if the doors could be plastered over and flush with the wall. However, I can’t find anything in our sizes of 20x30 cm (8x12 inches) (formerly a decommissioned stove, possibly future fresh air intake for a wood stove) and 15x30 cm (6x12 inches) (exhaust for the living room wood stove).
Does anyone have experience with other aesthetically pleasing solutions, know of systems or manufacturers, or have any other ideas?

Thank you!