I usually try and google the name and a few plant types eg rose, clematis although the results can be a bit random.
But also try searching on the RHS site as sometimes you get plants listed from their plantfinder database - if from here it wont always have pictures but it wil tell you what there is and what nurseries stock it and you then have a definite name to google if it's something you might like. Their database is very comprehensive.
I seem to use their site a lot from my recent posts - I wonder if they pay commission!