From Little Rd and SR 52, head East on SR 52 past San Antonio into Dade City.
Follow 52 north on 21st St, East on Meridian Ave (still 52).

Turn left (north) on 7th St, aka US 98 N aka US 301.
Stay on 301 through Bushnell. Go about 6-7 miles past Bushnell.

JUST after the merge with CR 741, turn right on CR 470. This becomes 1st St,
which becomes CR 48. Go about 18 miles all in all.

Turn left (northeast) at SR 19. Becomes Ducan Dr.
Merge right onto US 441/SR 19. Go 1 mile.
Turn left at Lake Eustis Dr/Lakeshore Dr. (SR 19)
Turn left at Grove St. (SR 19)
Stay on SR 19. Go through Umatilla.

Once you see Lake Dorr, you're in the national forest!
Turn right at NF 445 (E/NE) - towards Alexander Springs.
It's 6 miles to Alexander springs.
OR, After about 5 miles, Turn right at NF-538 (SE).
At about 2 miles, turn left on NF-538A.
Ride it out (1/2 mi) until it turns sharp right. 

The river is JUST northeast of you.