Hello and welcome
Sadly there is no economical alternative. PVA cannot possibly stick a contaminated, uneven piece of timber onto a concrete floor (it has absolutely no gap filling properties whatsoever) whilst Evostick might work for a short while but would fail relatively quickly - even faster if you don't get all the bitumen off. You'd also need a heck of a lot of it. The stuff that's used for the job contains a filler or body agent (to take-up roughness in both floor and underside of the blocks). It also produces a more elastic bond than the original bitumen bedding which allows for some movement in the timber blocks so they shouldn't come loose in the next few decades.
I'm a joiner, not a floorer, but I have sometimes done parquet repairs. AFAIK there are only really three suitable adhesives available in the UK: Lecol 5500, Laybond L16 and Sika 5500s. They
all require that the floor is completely clean of bitumen and that it has also been completely removed from the backs of the parquet blocks (not some of it or most of it). That means you'll need to scrape each and every block with something like a
Linbide tungsten scraper (not exactly expensive) - then do the same for the floor. The floor then needs at least two coats of a liquid DPM to be applied (something like Lecol PU280 - which is also expensive) - the final coat should be sand blinded with dry sharp sand whilst still wet. It then takes about an hour for this to dry-out. The sand gives a good mechanical bond for the adhesive to take to. The floor must be vacuumed-out before applying the adhesive to it and spread with a square notched trowel (or alternatively the backs of the blocks are "buttered" with the same tool).
Whatever adhesive you use to fix your loose blocks you will get
NO guarantee from any manufacturer, so if your project fails... it fails...Trying to use the wrong materials for this task always results in a failure and is probably why there is so much badly repaired parquet out there
In terms of sourcing smaller quantities it may be worth your while talking to local trade flooring suppliers to see if you can cadge-up/beg/borrow/steal some ends of cans from them. In exchange for a bit of beer money a friendly fitter may well be able to help you.
One last thing - when using the correct materials the glue will go everywhere, so invest in a tub of wet wipes - because you
really will need them
