This is far more complex than I can easily answer. Basically you need to define your edge conditions more accurately. Is the disc behaving like a membrane? Is it pre-stretched? or is it a simply supported plate? or is it encastre (built-in) at the edges?
RD Blevin's "Formulas for Natural Frequency and Mode Shape" gives the following solutions for uniform disks simply supported
f(i,j)=((lambda(i,j))^2)/(2*pi*a*a)*sqrt(E*h^3/(12*gamma*(1-nu*nu))
i,j =0,1,2....
a=radius of plate
h=thickness
nu=poissons ratio
i=number of nodal diameters
j=number of nodal circles
lambda for j=0
5,14,26
lambda for j=1
30 48 70
I hope that gives you some rough numbers to work with.
Cheers
Greg Locock