Great source for titanium bolts and fasteners
 

They seem to be the lowest cost and fastest responding; seems like they OEM for other companies like Wheels Mfg:

http://www.mettec.com/

http://www.mettec.com/category/214

STD bottle cage bolts
Ti M5-.80 x 10mm TSHCS 130 Ksi
Item #: M5X10TSHCS
Titanium Tapered Socket Head (TSHCS) M5 - .8 x 10mm.Grip Length = 2mm - Thread Length = 8mm.Aircraft grade
$3.87 *

Long bottle cage bolts for bottle cages + accessories
Ti M5-.80 x 15mm TSHCS 130 Ksi
Item #: M5X15TSHCS
Titanium Tapered Socket Head (TSHCS) M5 - .8 x 15mm Grip Length = 2mm - Thread Length = 13mm. Aircraft grade
$4.06 *