Mickey2

My 99 stitches through anything that fits under the presser foot. You can fit it with large size needles, I have found some Chinese on the web that goes up to 130 and 140 (Flying Tiger / Butterfly, the same needles sold under various names). There is plenty of clearing for these sizes needle in the old cast iron machines, I have checked with model 99, 15, 66, 201,...), but be careful with zigzaggers and newer machines. Some 1950s zigzaggers can too. I think all the needle brands go up to size 120 so any shop with a good selection should have it. Schmetz and the regular brands are more finely made than the Chinese needles, which aren't as polished and smooth. I haven't had any problems with them, and they don't cost much.

For the 99, clean it, oil it and it should do five layers of canvas with out any problem, at least if it's not too heavy (within garment weight). Anything you can slip under the presser foot with out struggle should generally be fine. My Viking 21E is faster and noticeably stronger than some of the later 60s and 70s models. Size 110 and 120 are enough for most jobs, and it's mostly because of thread thickness and the larger needle eye I go any higher (and stitching through strange materials like card board and plastic).