I buy my strings directly from Kalium Strings.
These are the strings gauges that are on almost all Megatar instruments made before February of 2017:
Bass Bottom Tuning (Megatar)
Melody string gauges: .009, .011, .012, .016, .029W, .040W
Bass string gauges: .025W, .035W, .050W, .065W, .085W, .100W
"Inverted-Fifths" Tuning (Chapman Stick)
Melody String gauges: .009, .011, .012, .016, .029W, .040W
Bass String gauges: .095W, .080W, .060W, .030W, .016, .010
Always have your intonation checked after changing strings. If you use a different string gauge you must adjust the intonation.