After 6 months of waiting the little current meters turned up from Aliexpress so I can now make my 18650 charger.
I used a 4 x version of the holder I posted at DIY 18650 battery holder
I used 4 x the lipo chargers posted at LiPo charger group build? (each set conservatively to 500mA).
I used a cheap LM2596 chinese buck converter to drop 12V to 5V.
The aliexpress link is below, unfortunately these are the 10A meters, not the 1A version but a 10mA resolution is still quite useful.