i dont think there is an off the shelf series booster u can buy so building it might be the only option , money no object ? buy two airflex pods and strap them together ( actually i would consider that when i think of the time i spent building my last booster lol )
The other option is the three in series setup ashbys use with their own booster , its give u more power for sure , the lift is not as fast to rise though compared to four series/parallel ... and the airflow not as good