Could you not simply pay for the rifle yourself using a bank transfer and then have the lads at Redbeck package it well for you.
You can then arrange your own delivery using https://www.tntdirect.co.uk/
All the lads would have to do is give the gun to the courier when he comes to collect it. Probably also an idea to ask them to remove the stock from the action when packing it (not sure about specific import rules for Croatia).
This way, you are not relying on anyone else being responsible for the delivery of your rifle.