Eurocopter sold a kit called the "Sand Filter" that was installed under a service bulletin. We used one back in the late 80's early 90's. It eats up a good bit of power as most particle separators do.
I just checked the AFS site, but it appears they don't have one for the 105, you may want to check with them directly as maybe they have one under development.
http://www.afsfilters.com/products.html
Good luck,
Chuck