Another substitution from my old buffalo blog! ^_^
1. Pink peppercorns. These have the same peppery taste with a very slight sweet aftertaste. And they are, of course, pink. The inner core is dark like pepper, though.
These are not related to true pepper (piper nigrum), but are the dried fruit of the Peruvian pepper tree (Schinus Molle). This is a common landscaping plant in many areas of the southwest, so it may be possible to find these fresh, without the problematic cc or preservatives, and dry your own. We have a friend with one in her yard who saved a bag for us and it’s been lovely. We got in touch over the internet and when we were in the neighborhood – a state away – she had a bag ready for us. Great friend, eh?
Ask about pesticides used and get permission before picking, of course. Also, make sure of your plant identification, as a close relative relative, the Brazilian pepper tree (Schinus terebenthifolius), may have mildly toxic properties. Information on the latter is contradictory.
2. Although I haven't been able to try this (as I am allergic), I understand that kiwi seeds are rather sharp, with a bit of a peppery taste, if they are crushed. I have no idea how one would separate the seeds easily, however! Here's a website talking about the kiwi, with some information on the fruit and seeds: http://blog.thetravelcook.com/2010/07/23/spicy-kiwi-sauce.aspx
2. Another pepper substitution idea is dried papaya seeds. If you can have papaya, scoop out the seeds and let them dry, a food dehydrator on low works well. We let ours dry in the air, but we live in a very low humidity environment. They need to be ground like peppercorns, but will give you a mild peppery aftertaste, once dried and ground. If you have any OAS reactions to papaya, however, these will still give the same type of reaction (as I found out, unfortunately).