I live in Ontario, Canada, but am close to a US border, so make frequent trips for stuff I can't get here.
Quark is hard to come by over here, you may find it in some European marts. If they cant get it then I suggest using fat free Greek yoghurt, which tastes much better anyway. They should be able to get the Fage stuff.
I am surprised they can't get fat free yoghurts though, as I have seen no end of different sorts every time I go shopping over the border.
Also some supermarkets doing a foreign section and I have managed to locate scan bran in those on occasion.
Walmart do Turkey breakfast sausages which are 80 calories for 2, and work out as 0.5 syns per two sausages, so worth checking those out.
There is also no end of 100 calorie packs you can get for snacks, which are obviously 5 syns.
If they have a Trader Joes near to them, then tell them to check that out, they do lots of yummy healthy and organic stuff and their fat free greek yoghurt is delicious.
Also we are allowed whole wheat English muffins as a healthy extra B here, the 57g ones, so it is worth telling them about those. No pitta breads yet as far as I am aware though. Bread is a bit hit and miss, obviously you are allowed 57g of any whole wheat, but trying to find a loaf that has 2 slices for under 57g can be hard. Unfortunatley we don't get any cereal bars available to us as a healthy extra, I am sure there are probably some that would qualify, but the overseas list hasnt been updated for yonks, and trying to enquire with slimming world themselves is a waste of time. We do get a few different cereals though, mainly cheerios and mini wheats (any variety) (1 oz I think).
Feel free to let them contact me through my blog if they are stuck for anything else.