Derailleurs cassettes freewheels chains

My five year old Cyclotricity Stealth has a 6 speed Shimano Tourney RD-TZ50 fitted with a 7 speed freewheel. Finding a replacement is turning out to very difficult, finding a hanger for this derailleur is proving even harder to find in the uk. What I’d like to do is to share information about derailleurs cassettes freewheels chains, dealers replacements original equipment as I’m pulling my hair out here trying to find a simple derailleur for a five yr old bike.