Rose window. Something circular of the desired size, (I used hole drilled into the MDF, but tops from
a suitable container will do) then get an image of a stained glass window (I used a
section of a Christmas card, but loads on internet) Cut image to size of hole & stick
it in.
Church Organ. Look at Church interior bits that various MDF & Resin manufacturers do.
Gothic Railings. Look at 'O' gauge model railways. I used some from a Great Western canopy kit.
Lab. bits. . There is a company (others might be able to provide links) that does Mad Professor's
Lab. with lots of useful bits. I tend to put interesting bits to one side, & used parts
from some old pens, the bits that clip onto shirt pockets, as they were chrome &
ended in a small ball. Upside down (& added to some other interesting bits) they
made excellent Mad Scientist globes of electricity.
Hope this gets you started. I look forward to seeing your results.