Could you show pictures of the pump? There is likely a way to adapt something and make this work. 

This machine uses a very "generic" pump. It is NOT special to the model.

If you can remove the pump and take it to a spare parts supplier, they should be able to find a match.

Really your repairer could have done this for you, but many repairers don't want to get involved in sourcing suitable parts for an old machine. Most customers don't want to mess about chasing obsolete parts or substitutes, If it isn't a quick, easy, cheap repair, they would rather buy a new machine. It's like classic cars - one person disposes of an old car because "it isn't worth fixing," then someone else buys it, spends a bit of money fixing it up, and gets great pleasure from the restoration and the restored car.

I suspect you are going to have to do this repair yourself. It isn't hard. You can watch some Youtubes on how to replace a washing machine pump, to get your knowledge and confidence up.

I think this is the pump you are looking for - I don't guarantee that, you can ask the supplier if it fits your machine.

(click on link below.) It is a generic "Universal Japanese washing machine" pump. Part number is J002, you can google it to see if there are closer suppliers to you. The J002 pump kit has two pump front cover pieces - one straight and one turns 90 degrees. This can be swapped if needed so suit your particular machine.

It would be helpful to know what the problem (if any) is with the springs and shocks. On these old Hitachis they don't actually have shock absorbers, they have a rather crude plastic damper above the spring which seems to be very reliable.

I'd just replace the pump and see how it goes, it's quite likely the suspension is OK. These old Hitachis and similar machines (the same machine was also sold as a General Electric 600N)  do have very basic suspension that is a bit prone to bouncing around and rattling during spin, but that's just how they are. Of course I haven't seen your machine, and your repairer has, so bear that in mind. Fisher and Paykel top loaders have a similar type of suspension, they have a few decades of refinement but are basically the same suspension system.

good luck with it.

Oh and the "huge clunk" is completely normal. It's the spin brake engaging. These older machines engage the brake at the end of spin, when the drum is still spinning full speed. The brake action is quite violent and makes a loud noise, it is normal.

Later machines, they wait for the drum to slow down naturally after spin, and only brake when the drum is almost stopped. It's quieter and the brake lasts longer. (Though yours has lasted well.)

I like these machines, they were made very cheaply but to a high standard of engineering.