En-route maps are available in eAIP maintained by LPS SR.
You can find eAIP here AIM.LPS.SK.
After opening link to eAIP, click on AIP SR button located on the right side. Next click to blue button eAIP/Download. In eAIP SR online part, click on Currently Effective button. En-route maps can be found on PART 2 – EN-ROUTE (ENR) / ENR 6 EN-ROUTE CHARTS.