I think this can be done with arrayfun.
% Your inputs
A2 = 'Number';
B2 = '0123456789';
lm = char(randi([32 64],10,100));
% Make the thing strings you want to find
ABz = strcat(A2,B2(:));
% Find them
out = arrayfun(@(ind) strfind(ABz{ind,:},lm(ind2,:)).1:length(ABz),'uni',false);