I could roughly emulate an 8 Bit Digital Pot with 8 resistors, 8 small relays & 8 digital I/O
using (roughly) R, 2R, 4R, 8R, 16R, 32R, 64R & 128R in series.
If R=100 then 255 steps from 0 ohms to 25K ohm linear taper digital pot.
Each relay would "short out" one resistor in series.
Things the OP may have access to, today.
It would be a little rough, with uneven steps, unless Marianne happens to have 100, 200, 400, 800, 1600, 3200, 6400 and 12800 ohm programming resistors. (Only the 100 ohm is a standard value.) Also unwieldy with 8 relays, if she happens to have 8 small relays just sitting there waiting for this, which I very much doubt, and pin-hungry with 8 I/O pins.
It's more likely that she might have 100, 220, 390, 820, 1K8, 3K3, 6K8 and 12K resistors, for a crude approximation of the resistors, but the relays are less likely.
Who knows, maybe she does have it all just sitting there to make up a temporary circuit that can be 'tacked' in then removed when the digital pot arrives, but I strongly suspect that she doesn't.
Best bet is still to find a fast supplier, in my opinion. Marianne, is it truly that urgent?