Many years ago I was missing a sprue in one of their 1/72nd scale kits. I had moved several times, dragging my stash with me. I sent an email to Roden asking if I could purchase it, admitting that I most likely lost the sprue falling out of the box during its travels. I never heard back via email, but about 6 weeks later I had a cardboard envelope from Ukraine in my mail with the missing sprue. I would not expect they can do this any longer.
You might be able to find a whole kit cheap at a local or regional model show.
Stuart