Boyd's makes left hand stocks for right hand actions,but I have asked them about a LH/LH action stock and they said not at this time.
You might try Stockade Guns,Kevin custom makes composite stocks,mainly Savage,but will make them for other Mfg's.
Richards Microfit stocks also will make you one in wood or laminate,but they are unfinished and unless you are good at woodwork may not be what you want.They do make nice stocks,and have many different styles to choose from.
Richards Microfit Gunstocks
You might have trouble finding anything for your Thompson C/F in lefty.