I've run across an afghan pattern (tunisian) that reqs a flexible afghan hook of 35". The designer altered a store-bought one by adding filament length which entailed cutting, drilling, etc. Oy. (Avail flex afghan hooks seem to max out at 22".) Could you use a circ crochet hook instead (they run 40")?
Circular crochet hooks confuse me because they they have hooks at both ends. But one site I found says you can put a needle point protector on one end to stop your stitches from sliding off and use it for Tunisian crochet also.