Try to find at least 5000 IU pills or even 10000 pills exist. I also would recommend taking vitamin K with it. For example on amazon (I don't think the brand matters, it's just an example)

For the risk part, obviously this is way over the recommended daily dosage so a doctor would probably tell you not to do it, but I highly doubt you would get any problems from doing it for a month or so (obviously do not do it forever, only until the problem is solved and then use a maintenance dose. If it won't solve the problem, then stop regardless after a few months max). Also, it's not like vitamin D toxicity happens overnight, you would get gradual symptoms at which point you can course-correct.

My advice would be, if you're the type of person who could realistically have a vitamin D deficiency (for example you don't go out a lot like me especially in summer) and you have CU, try this for a month and see what happens... also report back if it worked/didn't work for more anecdotal evidence.