Hi all!
Check with Janaka Motors in Panchikawatte... they have all original and Taiwan/Korean parts (barring the silencers) for quite reasonable prices.
Regarding the silencers, i suggest a walk up and down Panchi and check out all the used parts places. they are desperate for a sale and so will definitely be able to find you a decent set of used silencers.... then its up to you and bargaining. it's amazing the prices you get some stuff which you never thought you'll find here.....
the CB 125T is a very good and reliable bike and therefore there are quite a few on the road, so parts wont be hard to find....
all the best with the project!!