RE: 1999 21' Chinook Concourse parts
unless it is a terribly convoluted part, i suspect a local machine shop could fabricate one easily enough
i'd check phone book and call around before going to any of them to make sure it's the kind of job they handle - most shops have gone to CNC work which means they will need a decent quantity of something ordered to justify the set up costs
but there's always one or two shops that handle what we calll "one off" work
the rubber bushings they should also be able to match or approximate - one good source for a lot of items like that is
www.mcmaster.com
if you go to that web, don't be put off by the first page showing plumbing parts - punch in rubber or polymber stock in the search engine and you'll be overwhelmed with choices - they are to machine shops and manufacturers what sears & roebucks used to be to the retail market in the 60s - they have everything. You;ll need to know the durameter or hardness of the existing bushing and simply order the bar material, cut and bore it to your application's needs or the machine shop will be able to.
prices are retail (relative to jobber pricing) but what they offer is availability and service - i've ordered from them on a monday and had it here on tuesday shipped ups ground - if they get the order by 2:00PM it will ship the same day
i realize an off the shelf bracket from chinook would be easier, but in case, the above should help get you back on the road