it would be my Dolmar/Makita EA3400.
Must be a new model

.
The 421/4300 is a great budget 40cc saw and they are quite durable, but a little heavy for their cc size, although for their size they have nice power. They should mainly need things like filter, fuel lines, and spark plugs, and air filters which are found anywhere, other parts should be easily found on the net, which I find convenient as most dealers around me are almost worthless.
The echo line of saws is great also and similar as far as parts and quality of build. Not sure where the echo is built, but the EA4300 is built in china

, the previous version of it the dolmar 421(same saw different color) was built in Japan

iirc.
One thing nice is both have a standard carb so you don't need the dealer to assist if a problem arrises.
That being said I don't know if you will be able to find a part other than on the net 40 yrs from now.