I used to fit these week in week out years ago. Not the Wickes ones though.
I think you'd struggle to get that size now. I had to do a similar repair recently but they were 300x200 bumpys.
Anyone, I used to get my tiles through Graham's plumbers merchants, who were (and maybe still are) part of the Saint Gobain group, which CTD fall in the same group.
So, short answer, I'd try CTD lol