Availability of these systems is intermittent. Many parts are available. Military is no longer surplussing them in usable condition. (They damage them before selling).
eHam review∞
K4MG AB-577 web page∞

This all-aluminum military guyed mast/tower extends to 50 or 75 feet. The sections are 5" diameter and 5' long. The launcher guides and lifts the sections as they are fed in from the bottom. The tower can be rotated from the bottom. The total system with all components and tools weighs about three hundred pounds and is about 8 feet long. It can be handled by (one or) two people.

• The guys are anchored 30 feet out from the launcher at 120 degree intervals (3 locations)
• Guying is done at several levels
• Eight sections of 5 feet 2 inch masts are standard
• Sections are positively clamped together as they are raised
• Diameter of mast sections is 5 inches
• Mast is rotated from bottom with lever
• Launcher has roller bearings, guy rings have bearings to allow rotation
• Extension kit extends to 70 feet (additional masts, clamps and guys)
• Can be erected by one person
• Lifting and lowering is done by winch
• Launcher (lower section) is guyed, tubes fed up through, clamped and lifted

Availability of these systems is intermittent. Many parts are available. Military is no longer surplussing them in usable condition.
The AB-621/G is a larger version of the AB-577/GRC but has a 6" diameter mast and greater capability. Also not very available (probably less available).

This all-aluminum military guyed tower extends to 50 or 75 feet. The sections are 5" diameter and 5' long. The launcher guides and lifts the sections as they are fed in from the bottom. The tower can be rotated from the bottom. The system weighs a couple hundred pounds and is about 8 feet long. It can be handled by two people.