Try Quality Machine Tools:
Their 11" Precision Matthews lathes are close siblings of the Weiss machines, the latter (depending on model) being a metric version of the former. The machines would definitely not share leadscrew, cross-screw, change-gear set, graduated dials, etc. but they may well share other components.
Matt at QMT has generally exhibited a friendly attitude about helping people with machines he didn't necessarily sell.
But it may prove difficult to determine in advance which PM parts would fit which Weiss machines.