Shin splits are a bitch..
These days my cardio is hiking through the mountains
I was out there for 45-1hr a few weeks ago (we have snow season coming in so im not hiking right now), anyway an hour long hike, uphill terrain will be plenty for cardio
Or try walking around on treadmill/outside daily for cardio gains

No im not a fan of running..
Also, those walking stair climbers are a pain in the ass to go for a long time but they're worth it and can build up your cardio