Thanks Randy, I did another search as you recommended, and dumb me found the second switch. As you might expect, it was right in plain sight...the only problem was it was on the other side of the garage, by the garage entrance door...a place that's never used (I have only been living here 6 months). So, I still have no switch where it's needed. Now, the project has changed to a 4-way conversion. The complexity (and cost) is already starting to go up. :)

There are remote control switches that don't require wiring. Off hand, Leviton makes one but I don't know if works with 3-way.

You should be able to run a 12/3 cable from either existing switch to the desired location and make it work as a 4-way hook-up. The middle switch would be a 4-way and the other two would be 3-ways. The only added complexity from you original plan is that you may exceed the box-fill on that middle box.

Only other thing is that they shouldn't of used the white as a traveller but on the black screw (common) instead

200.7 Use of Insulation of a White or Gray Color or with Three Continuous White Stripes

(C) Circuits of 50 Volts or More. The use of insulation that is white or gray or that has three continuous white stripes for other than a grounded conductor for circuits of 50 volts or more shall be permitted only as in (1) through (3).

(1) If part of a cable assembly and where the insulation is permanently reidentified to indicate its use as an ungrounded conductor, by painting or other effective means at its termination, and at each location where the conductor is visible and accessible. Identification shall encircle the insulation and shall be a color other than white, gray, or green.

(2) Where a cable assembly contains an insulated conductor for single-pole, 3-way or 4-way switch loops and the conductor with white or gray insulation or a marking of three continuous white stripes is used for the supply to the switch but NOT AS A RETURN CONDUCTOR from the switch to the switched outlet. In these applications, the conductor with white or gray insulation or with three continuous white stripes shall be permanently reidentified to indicate its use by painting or other effective means at its terminations and at each location where the conductor is visible and accessible.

50% of the time, the common on a 3-way switch IS for the return conductor !!

What you need is to move the switch that is inside the house to inside the garage and next to the door between the house and garage. That way, you'd have a pair of two way switches in the garage: one next to the door to the house and the second one next to the main garage door. Unfortunately, that's tough to change now since the dry wall is installed and wall closed.

Thanks, everyone, for the valuable comments!