My 1972 Paramount included a Silca pump, please see the pictures below. It doesn’t produce air pressure and the main tube has a nice sized chunk missing. Can it be replaced or repaired?

that missing chunk only serves to help retain the threaded piece that keeps the pump's piston from backing out of the cylinder. In my experience, it is often damaged by folks who misuse the pump and allow tire pressure to flow back into the pump and shoot the piston out of the back of the pump.

Regarding the lack of pump pressure, my first guess would be that the leather washer that seals the piston isn't reliably contacting the cylinder walls. It might need a bit of grease to get a good seal. Or, you might need to flex the washer a bit to bend the sides of the cup shape outwards a bit, allowing it to contact the cylinder wall better.

I wonder if there is a Silca pump FAQ somewhere?
edit: Silca has this video describing how to condition the leather washer. Not exactly what I was looking for, but it's a start....

Steve in Peoria

Depends on why its not supplying pressure. The air is going someplace. It may just need the leather piston seal re-greased...
It can be used as is, just don't pull back so far.
It can be badly repaired with duct tape and spray paint. just to keep the top on, it doesn't effectively improve pumping.
You can come across replacements, both used and NOS, paint as needed.
Eric

PS I have a couple NOS leather seals...

Those leather seals are available, I got a couple off of eBay a couple of years back. IIRC, someone posted here that Silca, under the new ownership, was selling them again.
[MENTION=47570]Barrettscv[/MENTION], I am pretty certain that a Co-op would have some old main tubes, or even a few complete pumps that have other parts broken or trashed. The length of you existing main tube needs to be matched if its a frame fit model, I just sent my Silca to Grady (gomango,) and he fitted a longer tube from local Co-op to the workings so it would fit his frame.

Bill