Roof Crossbar replacement for bracket

We just bought this Jeep to tow behind our rv. Would like to have a kayak rack and see it has existing brackets as shown in picture. Anyone know what crossbar would fit on these angle brackets?

 

IMO the JK hard tops are not designed for heavy weight loads. There are more aftermarket roof rack kits for the 4-dr JKU that either attached to the rain channels or require drilling through the hard top with loads handled by an inner frame. From your pic the previous owner appears to have drilled through the hard top to secure those brackets and had to leave them there. Probably need to find out which aftermarket brand was used. Check out the roof rack offerings from venders like Quadratec or Northridge etc.