Are you buying from a local shop? The smallest they got in rats is 40g? All the places around me have every size mouse and rat in stock for frozen. Now live is a different story for small stuff as I have 1 place semi close to me that has pinkie/fuzzy rats all the time. I'm sure you can do every 3-4 days as I feed my little girl a 11-14g pinkie rat every 3 days till I get her filled out(got her just over a week ago) and she is 120g now. You can also just feed 2 mice every 6-7 days till he is big enough for those rats.