Iron core
Dayton Audio IC181-5 1.5mH 18 AWG Laminated Steel I-Core Speaker Crossover Inductor CoilDayton Audio 18 gauge steel I-core inductors are the most cost effective choice when large inductance values are needed for subwoofer crossovers. Features fully annealed refined copper wire with baked enamel...
www.parts-express.com
Air core
Dayton Audio 1.5mH 20 AWG Air Core Inductor Crossover CoilDayton Audio 20 gauge air core inductors are a great choice and the best value for building high quality crossovers. Features fully annealed refined copper wire, perfect layer windings and air core construction to ensure no hysteresis and...
www.parts-express.com
For the price I would get the air core. And replace the coil in both speakers so they match. It will hang off the board a little bit but that doesn’t matter. Glue that sucker on with hot glue.
How did you end up with a missing inductor?