I am so with you on this one! I could never find a twin trolley anywhere and ended up buying one of the things that you strap to your front, to put one of mine in and the other went in the normal baby trolley.
Now that mine are 3yrs and we have moved to country Vic, I can't use the one and only twin toddler trolley as only one side has straps. The other is broken.

I have to wait until there is somebody to come shopping with me, to push one in a stroller. As having a large family I can't put one in the trolley as I need the space for the shopping.
Next year should be better as I will be able to shop while they are at kinder.
But you would think that supermakets would cater for twins more as they are very common now. They want our money but won't help us by maintaining the trolleys that make shopping easier!