I am sorry to say there's no universal adaptor set - not just for this pram, but for no other as well. All car seat adapters are made so that the lower part fits the particular stroller's attachment system and their upper part the car seat attachment system. So each stroller has its own, different adapters - only some frames from the same brand or the same manufacturer (of different stroller brands) might be interchangeable. This is even more prominent with double strollers where the adapters are even fitted to the frame width and the different stroller configurations, so no way of going around the fact that you definitely need ONLY the Mikado Duet dedicated car seat adaptors.
In this case, the adapters are usually bought right when buying the stroller system - asking for them while buying the stroller at the given seller. What you can do here is pretty much just two things - contacting the seller you bought your pram at (or any seller of the Mikado brand), asking for the adapters to e ordered for you; OR contacting the manufacturer's customer service, asking for the same thing.
It might be that with such a low-cost, Polish brand, you won't be able to get them - but it's worth trying and you might get lucky, finding a helpful seller or service person. Worst comes to worst, browse classifieds to check whether someone with the same pram doesn't sell it, asking just for the adapters... if nothing, you'll simply won't be able to carry the capsules on the frame, just in the car (possibly getting a more lightweight, simpler pushchair for just traveling).