If it is that hard to get decent amounts of full fat yogurt, what about making your own from scratch, and then filtering out the whey?

That's a good idea, especially if you think it doesn't need to happen inside the fridge. Somebody on YouTube said it really needs only four hours to mostly drain, I suppose being on the counter for four hours would not create a bacteria problem. After all I suppose the true Greeks didn't use a fridge for this.

With more bulk I'd also need to go beyond the small strainers I have, I wonder if a colender would do the job?

I've been searching Amazon for frozen yogurt makers. The way they work is that you freeze a glycol-insulated bowl for a day beforehand then this machine does the periodic stirring while the stuff cools. The reviewers seem reasonably satisfied with the result, though they seem mostly sugar based. I may buy one of those, they're not too expensive. E.g. (US example)
http://www.amazon.com/Cuisinart-ICE-30BC-Indulgence-2-Quart-...