Well, U. longifolia is easy, but it is not an epiphyte.
In general these plants are difficult for beginners. You will find that those who do have them are reluctant to share the rare divisions possible with those with no experience, since it is likely that this would be a hard educational experience. U. asplundii is rare in cultivation. I suggest you find a start of U. alpina and practise with that species. Once you can demonstrate your abilities, you will be on the road, but I have to say these are some of the hardest CP to come by.
As to U. jamesoniana, the whole world is waiting for this little guy, and at present those hopes depend on several 3 cm cuttings held in loving trust by Pyro, Ron Gagliardo at the ABG, a grower in Germany and Holland, and my humble self. From us it will go to those involved with TC and to others with much experience with these plants. Hopefully it will only be a matter of time before it makes the rounds. Patience , grasshopper! We're working for you!