The Potter & Brumfeld T9A series is obsolete.
The process of searching for a replacement is best done by clicking the family breadcrumb link:
and start whittling down the list of options by making compatible selections from among the attributes that one cares about most, first. For example, the pictured parts have a 24VDC coil; an exact match would certainly be compatible, but so also would options rated for 24V AC or DC.
Something with a matching contact form would probably be needed. Probably want to match the coil type as well, and so on. The goal is to cast as wide a net as possible based on what your specific circumstances can tolerate, while eliminating results that don’t. Getting to a short list can happen faster than one might expect…
Eventually, for PC-mount relays one will need to start looking at datasheets to find options with a matching footprint. Use of the Series attribute can be useful at this point, to help avoid checking the same datasheet multiple times.

