It seems quite hard to get 6mm pipe insulation for 22mm pipe. Even Armaflex don't go that thin above 15mm pipe.
Found some (Alfaflex red sleeved):
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But I wonder why it's so uncommon...? If you use Talon clips (common) stacked, you get 35mm of space around a 22mm = 13/2 - 7.5mm thickness.
Even at such a thin wall thickness, online calcs show it roughly halves heat loss.