That is the auxiliary belt tensioner pulley.
On Lings they are £44.62.
Tegiwa also do them:
http://www.tegiwaimports.com/select...-auto-tensioner-pulley-civic-type-r-k20a.html
Jap Service Parts also do them
http://japserviceparts.co.uk/produc...da-aux-belt-tensioner-pulley-k20a2-k20z4.html
Or if you want you could just replace the bearing inside, but factor in by the time you pay for labour for the old bearing to be pushed out and a new one in, it might just be easier to replace the whole pulley.
http://japserviceparts.co.uk/produc...lley-bearing-honda-civic-type-r-ep3-k20a.html