Is that not Kappa's responsibility?
Presumably once the contract between Kappa and Roma is completed, Roma receive payments from Kappa and it is up to Kappa to sell as many shirts as possible to maximise their revenue from the contract. Consequently, maximising distribution should be Kappa's responsibility and obviously in their own interest.
However, IIRC, part of the value of the contract between Roma and Kappa is based on sales of replica kit, so maybe Roma should be doing more to improve distribution so that revenue is increased.
Funnily enough, and astonishingly to me, walking around the streets of Leicester (UK), the foreign soccer shirt I have seen people wearing most frequently is Roma's and it is widely available in sports goods shops in London also.