I got my ARUL from Model 1 Sales and it included the tube, spring, and buffer (as do all their ACE offerings). They had the best price and I received it promptly.
From their website:
ITEMPRICEQTY.
ACE ARFX Skeleton Stock, standard
Includes buffer tube, buffer & recoil spring
$90.00
ACE ARFX-E Entry Stock
Includes buffer tube, buffer & recoil spring
$100.00
ACE M4 SOCOM, 5 position adjustable, short
Includes buffer tube, buffer & recoil spring
$190.00
ACE M4 SOCOM, 5 position adjustable, long
Includes buffer tube, buffer & recoil spring
$210.00
ACE ARUL Stock
Includes buffer tube, buffer & recoil spring
$84.00
ACE Hammer Stock - OUT OF STOCK
Includes buffer tube, buffer & recoil spring
ETA: Brownell's states the Entry they sell does not come with the tube so make sure you check with the seller. From Brownell's: Pictured with Buffer Tube. Buffer Tube, Buffer, Spring and foam sleeve are NOT included.