Search this forum on saddle fitting. There's a lot of helpful information on where to start. You can narrow your search quite a bit by knowing:

(1) how wide are your sitbones?
(2) do you need a cut-out, or not (probably more likely in TT position)?
(3) "pear" shaped or "T" shaped?

That information (plus knowing that for long distance performance riding you want something very firm and as light as possible) should get you down to five or six saddles you think you might want to try. IMO the width and length of the nose is fine-tuning.

If many of your sister time-trialists have gone through the search without a trial program being available, then they must have lightly used saddles lying around their basements and garages. What about a team saddle exchange, formal or informal?

Also, in the US, if you order direct from Specialized, you can return the saddle within 30 days if you don't like it. Terry has a similar policy. Check whether they have the same policy in the UK.