For a CDN distributor of parts, I would think Solen (QC based in MTL) or http://www.partsconnexion.com/ (based here in Burlington ON) would do the trick to avoid border fees or high shipping - though I would comment that many times the shipping cost combined with lower prices in the US is the way to go, especially if dealing with an agreeable party who will send items to you USPS.
Back to the mods for the 60's.
Having complained that the 2 inch hole saw generated a hole too loose to press fit the stock front cup on my Grado's, I dug around in my speaker building box, and located my circle cutter - a variable sized cutting device perfect for use in a drill press, capable of making holes anywhere between 1-5 inches or so.
Some trial and error later, and I have some East Indian Rosewood cups that are the right size (with minimal Dremel work) for a press fit with the stock Grado cups. I received some of Tenzip's screens, and those should go right in there too.
Now we are getting somewhere - but I struggle with how to cut the 1/2 holes to allow the cables to escape - on my test cups, I have split off pieces of the edge of the cup, trying to use my drill press to cut a hole 1/2 or so centered on the edge.
My next thought is to clamp my 2 cups together, and drill down the middle of them, thus creating a 1/2 hole in each.
Is that how you guys do it, or are you using a Dremel, or did you mill that in before cutting the cups etc?