If you add your home town to your profile it gives other members an guide as to whether they could deal with you.
A divers bottle is a very heavy item and most would not consider posting.
The ideal setup for you would be a 12ltr 300 bar cylinder with a 5 year test certificate + ( if you can afford it )
A, 3ltr 300 bar for re-filling in the field.
Good luck with your HW100, great rifle, I have one and after trying most other makes, have found it the best.