CRG definitely has an extended front porch kit available. It’s priced at $345 at Acceleration Karting for a new kit. With that being said, I’ve seen a lot of tall drivers run without an extended porch just fine (you have the option to remove the foot rests to gain an extra few inches).
I have a complete CRG shifter kart for sale just in case you are interested… ;)
Be sure you need an extended pourch. My son and I are 6’2″ and 6’3″ and have run the extended pourch and liked it better without. There are thing to do to a chassis with out using the extended pourch. Seat and pedals. We run Birel chassis.