WASHINGTON -- Sean Matson, who recently left active duty as a Navy SEAL, said the military measured his head four times -- each time before deployment -- with plans to provide him a more advanced ballistic helmet.

But the new helmet never materialized. During a deployment in Africa, Matson and six of his fellow SEALs each shelled out about $900 for updated helmets that held the lights, communications devices and batteries needed for their missions.

"There was never a clear solution to it, so guys were going out spending $800-$900 on their own ballistic helmet," said Matson, who is now CEO of the military supply company Matbock.

Elite troops such as the SEALs are more and more forced to dip into their own pockets to purchase basic military gear such as helmets, global positioning devices and medical supplies, according to Matson and others involved in the military's unofficial civilian-side supply network who came to Capitol Hill on Thursday.

House lawmakers have taken notice and said they will request an explanation from Defense Secretary Ash Carter.

"These are the guys we assume have the best gear all the time," said Rep. Duncan Hunter, R-California, a Marine Corps combat veteran.

Hunter said special operations troops have been approaching him in his California district complaining about the inability to get needed materials and he has been investigating the issue.

Numerous individual instances point to a systemic problem in the military's supply chain, but a blind spot exists between Defense Department vendors and the troops who need the gear and supplies, Hunter said.

"It's been impossible for me to find out how the money is getting stopped and why it is not going down to where it's supposed to be," he said.

Aaron Negherbon is the executive director of the nonprofit group Troops Direct, which ships needed and requested supplies -- from boot laces to tablet devices -- to service members who cannot get it through their commands.

Less than two days after the attack on the U.S. embassy in Benghazi, Libya, Negherbon said he was contacted by the commander of a Marine Corps Fleet Anti-Terrorism Security Team that was being deployed there.

The commander told him the team lacked a variety of crucial equipment, including sniper supplies, he said.

"They came to us for ... batteries because they didn't have any of those. ... It is kind of like, 'What the heck is going on?' " Negherbon said.

He said troops often have to buy their own medical equipment such as tourniquets, and shell out about $1,000 each for their own helmets or $500 for a GPS device that they need for duty during a deployment.

"The question is, why can't you get this?" Negherbon said.

Often the answer seems to be a higher command does not have the money budgeted or the equipment was approved but not available from vendors.

"That is a good thing, we know where the problem is, but [those issues] are very profound," he said.

A small group of House Republican lawmakers gathered Thursday to hear the concerns.

Rep. Adam Kinzinger, R-Illinois, an Air Force combat veteran, said the military has to weigh the concerns of supplying needed equipment with the desire of troops to always have the newest gear on the market.

Still, Kinzinger said the shortfalls in the supply chain could become a major issue if deployments ramp up again to the levels seen during the height of the Iraq and Afghanistan wars.

Rep. Chris Gibson, R-New York, an Army veteran, said the group should write a letter to Carter, saying they have serious concerns about supply breakdowns, including the inability of Matson and his fellow SEALs to get helmets capable of mounting lights, though the equipment was approved.

"If you've got a situation where unit is approved for an Ops Corps [brand ballistic] helmet and it's not getting it, we need to understand what the problem is ... that is unacceptable," he said.

Related video: