The prices on lion brand 24/7 on amazon look high, I would guess it could be an indication of it being discontinued.
On woolwarehouse there’s a search bar at the top. I out in “mercerised cotton” the used the filter for DK weight and got these results
I would base my decision on what colours you want for the map, some have a lot of colour options.
I can’t really recommend a brand as I’m not experienced enough to have used them. I have used the Drops muskat though and it is gorgeous looking, has a sheen to it, the colours are strong and the stitch definition is lovely…but you might want something softer looking/feeling.
If you are substituting yarn I personally see no reason to stick with the fibre in the pattern unless it has a particular quality you want to duplicate (like mohair). The map sweater would be just as lovely in wool, acrylic, a blend, a recycled yarn. Maybe choose a DK yarn based on what you want from your sweater, then swatch for gauge.