wirelss backup without time capsule

Time Capsules are still available on sites like Amazon or Ebay in new and refurbished versions, so if you have had good luck with your Time Capsule, you might consider adding another before the stock is depleted.

There are no other manufacturers that offer a product just like the Time Capsule that combines a wireless router with a built in hard drive.

If you don't want to opt for another Time Capsule, you will need either a new router with a USB port to connect a hard drive to that will support Time Machine backups.......like the Synology router or some of the upper end Asus routers. So, two separate products.....a router.....and an attached USB drive to the router.

Or

Assuming you already have another router, you will need a Network Attached Storage (NAS) device that supports Time Machine like the Synology products. The NAS connects to your router using a wired Ethernet cable connection, but the Macs will back up over the WiFi provided by the wireless router.