has anyone fitted the larger bolt handle from the SSG police to a pro hunter? were can the large handle be bought from?

You might try asking the Steyr factory, since you are on the East side of the Atlantic. Here in the USA there are no sources of spare parts for the Steyr products (thanks to foul ups in their USA marketing over the last almost 10 years). Those large pear shaped bolt handles are deceiving, and sooo sweet!!
LLS

Fr Frog has the large, round bolt knobs for the Steyr Scout/ProHunter.

http://www.steyrscout.org/project.htm