Akrapovic exhaust works with their optional aftermarket cat p-kat-028, refer to installation pdf:
http://az79640.vo.msecnd.net/akrapovicbppmultimedia/6126528246204bcd802a22083352bde6.pdf
Arrow exhausts also manufacture aftermarket catalytic converters for their pipes, and they have one for their CBR250R pipe:
http://www.emlineamoto.com/en/exhaust/catalysts/11010kz.html
500 exhaust wouldn't work because, as previously mentioned, the cat is before the pipe on this one (directly under the engine).
The new 300 exhaust might work if you'll wait for it, but I doubt that will weigh much less.
Pointing out exhausts that don't have cats really doesn't answer the OP's question at all.
http://az79640.vo.msecnd.net/akrapovicbppmultimedia/6126528246204bcd802a22083352bde6.pdf
Arrow exhausts also manufacture aftermarket catalytic converters for their pipes, and they have one for their CBR250R pipe:
http://www.emlineamoto.com/en/exhaust/catalysts/11010kz.html
500 exhaust wouldn't work because, as previously mentioned, the cat is before the pipe on this one (directly under the engine).
The new 300 exhaust might work if you'll wait for it, but I doubt that will weigh much less.
Pointing out exhausts that don't have cats really doesn't answer the OP's question at all.
