Alpha RV16AF are mini pots, 16mm diameter. Normally around the £3 mark. Available for solid or spline knobs, with solder lugs, pins or PCB mount.
Alpha RV24AF are the full size version. Around £3.
NW Guitars sell them, along with plenty others. Products all have the tech drawing so you can pick the correct size.
https://northwestguitars.co.uk/collections/potentiometers?sort_by=best-selling
Bourns PDB241-GTR
https://www.bourns.com/docs/product-datasheets/PDB241-GTR.pdf
£4 from Farnell or RS Components but £4 delivery.
Banzai Music in Germany carry all the MEC potentiometers; not cheap.
https://www.banzaimusic.com/MEC-c-176/
Musikding, also in Germany sell Alpha, Bourns and CTS. Great company, no VAT worries, fast shipping, fantastic prices.
https://www.musikding.de/Potentiometer_1