When I replaced the bedroom slide seals on my 2000, I purchased them from Monaco. If Monaco is not up and running Beaver Coach Sales in Bend Oregon probably has the seals.
The seal is sold by the foot, so you will need to know how many feet of seal you need. You should be sure that the slide is centered in the opening and aligned properly, as improper alignment will cause early seal failure.
The seal is not to difficult to replace, just time consuming taking off the old glue. The new seal will come with a pressure sensitive adhesive already installed on it and you will have to cut them to fit.
Gerald