The rarity of Patrat on Route 1 is, Very easy to encounter. I met one but then I can't find Patrat someone help me what keeps appearing is Lillipup
On route one here are the rarity percentages:
Lillipup 50% Patrat 50%
So if you percivire you will find one. Here is the link to route 1 info http://pokemon.marriland.com/black_white/walkthrough/triobadge/route_1