I don't know of anywhere to get a 2 or 3 pices ramrod from made from brass.
A length of 5/16" (.312") brass bar would do for most calibres. A wooden door knob on the end would stop it blowing the rod through your hand if you had a premature discharge while loading. For a bore guide you can either use a suitable cartridge or get one turned down from brass or aluminium. You could also find a piece tube that will fit into the bore and flare the end of it so it does not drop into the barrel. Plumbers use brass reducing bushes that might be suitable. All you would need to do is file the threads off the outside to tidy it up.