I don't know of any US programs that offer a non-residential, thesis only ThM. Westminster has a modular one in London, but it still requires coursework before the thesis.
Outside of the US, you have quite a few options for part-time, non-residential, thesis-only MTh programs (the nomenclature overseas is MTh, not ThM). Note, these are not all or even mostly explicitly Reformed programs.
-London School of Theology
-South Africa Theological Seminary
-University of South Africa
-Wales Evangelical School of Theology (pretty sure they have it)
-North-West University (SA)
-Greenwich School of Theology
-Spurgeon's College
-Highland Theological College (I think they offer it, though they require some residency for PhD, not sure on lower than that)
