Hello,
I maybe able to help. We have many Morus alba specimens growing here, both planted and 'occurring.' It is a somewhat invasive plant here. The best examples we have here were not planted, but were left rather than removed. We also have Morus rubra growing here. You could have seed from both.
If vigour and taste are what you are looking for Morus 'Illinois Everbearing' is the best for us. You can have seed from that as well. Cuttings are possible, but will be complicated. You can maybe tell me what the rules are for material entering your country. Let me know although with a metre of snow on the ground and last night's low of -22C we are not in a rush.
Take care,
Robert