Electrolux Masterlux shampoo tank – can we adapt something?

We have been given an Electrolux Masterlux cleaning system wet, dry and shampoo cleaner Model Z76A Product 9009430-01 which I see from this site is very old and that parts (except bags) no longer seem to be available. Whilst it’s old in age it is as new in condition and works well on most functions but I see from the manual it has a vital part for shampooing missing – the shampoo solution tank which looks rather a large part! Does anyone have any idea where we could find one or would it be possible to adapt something else? ❓