air filter and issues.

Can you guys point me to the right place to buy a replacement foam rather than me forking out best part of £200 for a complete new intake, thanks.

i resently put a HKN mushroom filter and dump valve and when im in between gears - gear change my revs drop as low as the engine stalling. do you know what might be the issue. im thinking the air flow meter sensor but its conncted ??? im puzzled.