Is there anyway to find out the cause of idiopathic leukocytoclastic vasculitis and treat that naturally instead of going on methotrexate?

No and yes: Certainly the known possible causes of lcv should be looked for but if it is determined to be idiopathic, the cause is unknown. Treatment ranges from no treatment required at all to Methotrexate to other medications. Natural or herbal remedies have not been shown to have any conclusive effect but then again, medications are not always required. Mention your concerns to your doctor.

No natural Rx: This type of vasculitis can be secondary to several causes including viruses, allergies (especially reactions to meds), infection and even malignancies. There are no natural cures. Sometimes if one can establish and treat the cause then the rash can improve.