After racing this Sunday, it is clear that my weakness is 30 - 60 sec power climbs 
. I have another big race in a few weeks - which workout would help me improve? (I’m not yet familiar with all the workout names, sorry, and I couldn’t see how to search the database using interval duration).
You will want to be doing efforts around the duration of the climbs that you struggle with so, 1 min-ish and just choose anaerobic capacity in the search filter this should bring all these types of workouts up.
It also depends a lot if your weakness is doing a single 30-60 second effort, or if you have a hard time repeating this over and over on short rest.
Depending on which it is, train appropriately. 30-60 seconds hard followed by a long rest is highly anaerobic. 30-60 seconds hard followed by a short rest is highly aerobic. They’re both hard, pick your poison.
As for searching, click workouts, select one or more of VO2max, anaerobic, sprint. You can type search terms in such as: 30-second and rides with that description will pop up. Still takes some manual browsing through the results, but it’ll narrow things down a good bit.
Have a look at the Rolling Road Race specialty plan.
Loads of workouts that are perfect for that kind of race.
I suggest you find a quiet road approximately 20 minutes away with a 5% gradient. Ride up at just under your maximum, noting where you started, like a layby. At the end of a 60 second effort note where you finish, then return safely to your starting point and crawl to the starting waiting for the 1 minute timer to tell you when to start again. Repeat until you’ve done 10 efforts, or do 5 , rest a little longer then do another 5. This will adapt your body more readily than sitting on your turbo in my opinion as your pacing will need brain power than looking at a wattage number.
30-60s efforts!! Be race specific!