I spoke to Chris Coaster at the Meridian Repair shop about M100 grill cloths. He suggested Nexxia acoustic fabric, which stretches in two direction, and so works well for the complex shape of the M10 and M100. I put a description here, along with the contact for the person at Nexxia:

M3 Refurbishment

Since I live close to Nexxia, I dropped in and got several sets of their fabric. Then I got distracted repairing the grill frames of a pair of M20s so I haven't yet refurbished the M100s. The cloths I have for the M100s are CT 64-01 (black) and CT 64-05 (red). I have just tried fitting one of the cloths and they work fine. The thing to note is that the original cloth covers the top, sides and front, but not the bottom of the M100 grill frame. On the bottom of the frame, the cloth only covers the small section at the front. What I have not yet done is draw a template for how to cut the fabric.

If you haven't seen how the original grill fabric was attached, I can take a couple of photos.

- Zygmunt

Living Room: Michell Focus One/Focus/AT30E 101B M2 (from new in 1983-85). G91A-DAB (family friendly).
Office: rMB12 596 504 502 M30
Other office: AD88
Studio: 104 101B M100 - For Radio 3 Choral Evensong !