The problem is those pipes are being sold on Asian market like in stores not even online , i have checked philippines website for bike sales - there are about ¬20 pipes for 125-150. The problem is you cant get them , unless you find a guy who sells it and can ship it to Europe. As you said that stock pipe is heavy , which means modifying it wont help much. Im cracking on ebay right now , messaging every single Asian store.
Do you have any idea if that twobros or yoshimura exhaust is heavy?