Hetre are a few yards with Sport Tracs in their yard listing an exhaust manifold, (I can not look up th Y pipe itself).
2001
Exhaust Manifold
Ford Explorer Sport Trac L.4.0L ID..CE A HC0016 $199.12
--Can--
$225.01 Bastarache's Auto Salvage Can-NB(Shediac-River) E-mail 1-506-532-6621
2001
Exhaust Manifold
Ford Explorer Sport Trac CHK ID WHEN OUT A A31436 $75 Jones Auto, Inc. USA-IN(Orleans) E-mail 1-812-865-4161
2002
Exhaust Manifold
Ford Explorer Sport Trac 5-02,TBI,4.0L LEFT B FE6193 $66.37
--Can--
$75.00 Nieson Auto Wreckers Can-ON(Cambridge) E-mail 1-519-621-3240/1-800-265-9817 (ON only)
2002
Exhaust Manifold
Ford Explorer Sport Trac 4.0 SOCH 05-110 $50 I 40 Used Auto Parts USA-NC(Morganton) E-mail 1-800-222-0410
2002
Exhaust Manifold
Ford Explorer Sport Trac CAST#RF1L2E9431CB M00515 $50 Stricker Auto Parts USA-OH(Batavia) E-mail 1-800-582-5405
This should give you a few options.