Hi Andy
The 33.7 X 2.5 tube should be fine & as far as I am aware, this is the size tube that most manufactures use for the wishbone bush tubes.
33.7 X 2.5 is a standard stock size & as you have found out, the next size up is 33.7 X 3.0
Most unlikely that you will find any sizes other than standard stock.
The thing to remember is,
all steel sizes are nominal, they can and do vary from batch to batch/manufacturer to manufacturer
I used 33.7 X 2.5 ( Nominal ) for my tubes & the bushes fit just fine & to be honest, wouldn't want them to be any tighter than they are.
Hope that is of some help
