check on the business link website they have a link to a goverment tender site supply to gov or something. Then just edit your preferences so that you get info from the relevant authorities if the tender seems suitable follow the info given to get a pre-tender qualification pack.
Also check your local authority website, do some calls and make yourself and your business known to the contracts procurment teams, then if anything comes up they have your name and will recognise your business in any tender applications you may send.
Hope this helps