Finding a motor other than the original to fit the frame's unique housing seems unlikely. Mid-drive bike manufacturers worth their salt design frames around each motor model's specific shape and mounting points.
There's a chance another model of motor from TranzX would fit, but then there could be an issue with display compatibility. That's a question TranzX customer service folks might have a hard time answering, let alone someone here. I do know that most new versions of motor models from Bosch, Shimano, Yamaha etc are incompatible with old frames and displays.
Raleigh Electric almost certainly probably won't have a solution, and if you're in the USA, there's no one to ask as they've pulled out ot the market. If your 2018 motor has failed, that really sucks - hopefully TranzX has a replacement for you.