We propose a novel dual-function radar-communications (DFRC) system that relies on multiple intelligent reflecting surfaces (IRSs) to enhance detection of non-line-of-sight (NLoS) targets. In particular, we consider a wideband OFDM transmit signal for which we jointly design the frequency-dependent beamforming and phase shifts to maximize the average SINR of radar and the minimal communication SINR among all users. We solve the resulting highly nonconvex problem comprising maximin objective function with a difference of convex (DC) constraint through an alternating maximization (AM) framework of alternating direction method of multipliers (ADMM) and Dinkelbach's method. Numerical experiments demonstrate that the proposed method with multiple IRS can achieve 3.3 dB radar SINR enhancement and 0.9 dB minimal communication SINR improvement compared with single IRS scenario.