I have 2 mixers (good thing about them is you only need one beater), and I always put the call out for students to bring one in. I usually have 2 kids remember to bring a mixer, and after 2-3 class periods I send the extra mixers home and we just twist with the two I have. I avg. 24 students in 6th grade at one time. I also put the call out in advance for students to bring in crepe paper streamers or to buy a roll or two. I buy some from classroomdirect.com in some of the odd colors - brown, gray, & peach - and require the students to scavenge other colors. So far I haven't had any problem with this method. :-)
How many mixer do you have?
How many kids do you teach in 6th?