It seems, Goodhifi doesn't align or shim anything.
That's asking for trouble with most drivers but that's probably just me...
You can buy foam rings everywhere and in many different qualities.
Some almost fit the drivers they were bought for.
But please understand that what you are buying are spare parts, which means that it
will take some kind of skill, education or at least a minimum of training to replace the parts.
I have done loads of drivers and I've thrown away hard-to-find original drivers that were destroyed
by owners wanting to have a go at repairing themselves.
No shim'ing, a skewed spider or deformation of the coil combined with the use of wrong glue often puts
the driver in the bin as unrepairable.
I am not saying that you can't do the refoaming yourself and if you would like to try your luck then the
S45's makes a good choice since the tolerances are pretty open and in case of a total disaster, a new pair
can be found quite easily. Of course, it will still be a waste of money and time and you will have to do the
new pair as well - only better.
I would recommend you let someone who knows how, get it right for you the first time.
It's not an expensive repair and worth it if you like the speakers.
Martin