JJ, its very kind of you to consider this - but it might be that this man can actually cope. Mr BM has had issues with his knees and spent 8 months on crutches 2 years ago. He has been on and off crutches since Christmas waiting for an op.
Mr BM was a hulk of a man in earlier days and a very good footballer (hence the damaged knees). He can look quite unwell hobbling on crutches, and it looks as if he is struggling, but I know his true strength. The crutches get in the way of what he wants to do because they are an inconvenient necessity. And it is not easy to look competent even on one crutch.
Rather than simply buying something he may not use - why not have a chat to him? If you say you have a spare one which might help, he might be more inclined to accept it if he really needs it. I do know that if someone gave Mr BM a shopping trolley, he'd be horrified - since he can manage it just looks awful. I think the key here is communication.