Is there a conversion table for the above three different paint manufacturer so that I can
check colors between them
You can use the cross reference charts at Humbrol’s site to match Humbrol to a number of other manufacturers (Mr Color is not listed)
http://www.humbrol.com/convert-to-humbrol/conversion-tables/
You can also try http://www.paint4models.com/index.html which covers a wide range of paints, but the listings can sometimes be close matches rather than exact matches.