Easy enough to get consumables for servicing (e.g. oil filters, air filters, belts, rollers, bulbs, tyres, batteries, brake pads) as they share parts with other Kymco scooters, including the newer DT350i. A bit more difficult to get specific parts such as fairings, windshields and plastics unless you're willing to pay a premium from online international suppliers from Taiwan or Europe.
LEA7 is the code for DT300 parts,
ACD5 is the code for DT350 parts.
Otherwise the DT300i is a reliable bike, only minor issues. This thread will give you some details.
https://www.kymcoforum.com/index.php?topic=23676.0