Despite recent events, the Fairyland CDC "does not know of a virus, condition or curse that would reanimate dead gnomes (or one that would present zombie-like symptoms)."
Zombie Garden Gnome (Cheaper but not as cool) [Amazon]
Official Gnombies homepage [thegnombies.com]
Garden Gnome Zombie T-shirts, etc. [Cafepress]
Alternatively, there is a "Mini Zombie Gnome Hand-Painted Blood Bath Creature" available at Etsy.
Previously: CDC explains how to prepare for a zombie apocalypse, Zombie garden sculpture brings the flesh-slavering undead to your daffodil bed