You can use the ones that you made with a pencil if you cannot find the smaller ones. That way they will not go to waste.
I also had a problem in inserting the cane, especially with the cellophane wrapping, but I was determined it would be made to fit! - I pushed a biro pen through the loops and stretched it as much as I dare - being felt there is a little bit of give in the material - and I managed to insert the cane. The next one I make I will just move the felt a bit below the first stitching line which will make the loops a bit bigger.
The ones I bought in The works last year fitted the designs although the posh ones from Thorntons were much too big.