On this excellent website you can go to “Seats A to Z” and look up the declared candidates in your constituency, as well as much more information. However, this site does not include contact details for candidates.

Finding contact details for candidates

The vast majority of candidates now have their own websites or sections on their local party website, on which they will display their contact details. A very good list of candidate websites is available here courtesy of Political Science Resources.
The new Your Next MP website, which includes most candidates and their contacts, is very useful too.

Alternatively, candidate websites can usually be found by a simple internet search. In your search engine, key in your constituency name followed by “prospective parliamentary candidate” or the name of the candidate if you know it. For example: “Brighton Pavilion prospective parliamentary candidate”. Sometimes you may need to refine your search by adding the party you are looking for. For example, “Brighton Pavilion Liberal Democrat prospective parliamentary candidate”.

The three main parties have full listings of their candidates on their websites. Most of the candidate entries include contact details: