Could you calculate a Histogram and then look for the maximum with WaveStats?
Beside the command line both operations can be accessed via Igor's Analysis menu.
A.

A neat stats trick is to use something called the "shorth":
DF Andrews, “Robust Estimates of Location.” Princeton University Press (1972).

This can be implemented in Igor as follows:

function shorth(data,alpha)
	wave data
	variable alpha
 
	duplicate /free data,sorted
	sort data,sorted
	variable n=numpnts(data)
	alpha*=n
	make /o/n=(n/2) shorths=sorted[p+alpha]-sorted[p]
	wavestats /q/m=1 shorths
	variable meann=mean(sorted,v_minloc,v_minloc+n/2)
	return meann
end

Alpha=0.5 is the typical choice. This code then finds the mean of the data in the shortest interval that contains half the data. So it is robust against modes that are not the main mode. This does not return the mode per se, but it is an estimator that asymptotically approaches the mode, and summarizes the data a little bit more cleanly in my opinion.

Rick