For miniatures in 28mm, have a look at Underfire Miniatures. They have US, Soviet, Germans (both sides of the IGB) and have mooted British (but Empress is committed to do BAOR in 28mm). They have also Rhodesians and FRG Polizei. Link: http://www.underfireminiatures.com/
As for vehicles, butlers printed models offer 3d printed cold war stuff in all scales. I have several 15mm models and are good. I have been told the 28mm stuff is even better because print lines are less noticeable. They do 1/56 and 1/48 to satisfy both sides of the 28mm debate. They have Dutch, Danish, Italian vehicles that no one else does in 28mm. They also have Canadian stuff, and IDF conversions. An S tank and PBV302 too! Link: https://www.butlersprintedmodels.co.uk/
Badger games in US also has the old Mongrel (not mongol) range. They are nice miniatures, many sculpted by the talented Paul Hicks. I got aplenty when Frank Hammond (the original UK owner) was still at the helm.
As for scale, some people does individual based 12mm (and timecast models are great) so it could be an option. Otherwise right now 15mm, and 28mm are decently served, 20mm has always been. Spoiled by choice! To be quite honest 28mm is nice for very small encounters, but for engagement like the one presented in the old GDW Last Battle scenarios, probably 15mm is better. Except if you have both a mega table and mega terrain.