We did a job with Andy Lewis and this is how we set up temporary slacklines without trees. The bolts we used were https://www.amazon.com/gp/product/B005EH2N5E/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1 and the chains I used were the cheap 400lb rated ones from my local hardware store. Any slackline outfitter has slackline kits you can buy to get started.
A more permanent slackline can be rigged without trees by building "dead man anchors", where you bury something and wrap a chain or rope around it and that becomes your anchor on either side.
Check out https://www.slackademics.com/ to learn everything you need to know about slacklining and highlining.
Thank you for the support!