Are there any natural (holistic) supplements I can take to help lower my blood pressure?

Yes. Blood pressure can be affected by various supplements, but the easiest and least invasive way to lower blood pressure is to reduce the body's response to stress. Techniques such as heartmath guided imagery (heartmath.Com) have been found to be effective.
Sometimes. Most nutritional supplements do not satisfactorily lower blood pressure that is markedly elevated. Olive lead extract supplements reportedly reduce mildly elevated blood pressure as effectively as an ACE inhibitor. This has been the case in my medical practice for most individuals. As with all medical condition, addressing underlying causes is the most important strategy to solve your condition.