sprocket size?

Ok,

a while back i bought a bike. had a 525 chain and (i believe, as there is no where to tell) a matching 525 drive systems rear sprocket. When i bought the bike the chain was pretty much done. So i bought a new one. pop it on, ensure everything is good to go, straight, tight, and aligned.

now when i coast to a stop i hear a kind of dull rubbing/clicking, it is there only when i slow down, not when i speed up , (engine under load)

so i'm thinking maybe the front sprocket has some worn teeth on it. Pull the cover off, and it is in fairly good condition, no broken teeth or anything. However the front sprocket looks to be the OEM for a 530 chain. I am wondering if this would cause the sound i am hearing.

second question is: i can't for the life of my find a damn 525 16t front sprocket anywhere online. all i can find it 520 conversions or 530 OEM gearing. so am i just no good at searching online or will a 520 be fine? or is my problem not related to the front sprocket size and i should go back and check alignment again (think i will do that anyway)

anyway, you help is appreciated.