What gun are you having problems with ??
Pretty much every gun out there is easy enough to service and look after by yourself. If your part of a team with a Gun deal, there is normally one of the team thats pretty good and knows all about that marker.
I have never used them or owned either gun but I know the Planet Eclipse do servicing and believe that Dye do to. Some of the site advertisers at the top of the page sgould be able to help as well. If your going to a "Main" type of Tourney event then most manufacturers normally have some sort of on site gun techs.
Failing that Youtube is your friend or dare i say it PBnation !!!