Are you sure you can only go up to 9x13? That seems odd for any enlarger. If that is indeed the case, any of the 40mm lenses will get you into the 11x14 range. A less expensive solution would be to physically increase the space between the bottom of the enlarger column and the baseboard. A few thicknesses of MDF would do the trick. You might even find some cutoffs in the scrap bin at the Home Depot (by the radial arm saw).