The Mets are “actively” looking to trade one of their veteran starting pitchers, in the estimation of one industry source, and they are hopeful next week’s Winter Meetings clear up some of the pitching gridlock slowing down all teams interested in acquiring or dealing arms.

As The Post’s Joel Sherman reported on Sunday, the Mets intend to unload one of the trio of Bartolo Colon, Dillon Gee or Jon Niese by the start of the 2015 season. They already have engaged clubs on this matter, although they aren’t believed to be far down the road on any specific trade.

None of the three is likely to bring back a particularly robust return. Instead, giving up a veteran arm could help the Mets plug holes elsewhere (lefty reliever, bench player or prospect) and give them some payroll flexibility. If they are to find a shortstop in this market, which will be no easy task, the Mets likely will have to use another resource, be it money or more valuable trade chips.

Colon, 41, led the 2014 Mets with 202 ¹/₃ innings and put up a high 4.09 ERA, striking out 151 and walking 30. He is due $11 million in 2015 after signing a two-year, $20 million agreement with the Mets in December 2013.

Gee, 28, made just 22 starts last season due to a strained lat muscle and when he did pitch, underwhelmed with a 4.00 ERA, 94 strikeouts and 43 walks in 137 ¹/₃ innings. He will make about $5 million through the arbitration process in 2015 and is eligible for free agency after 2016.

Niese, 28, has a contract keeping him under team control through 2018 (there are team options for 2017 and ’18) and will make $7 million in 2015. He tallied a 3.40 ERA in 187 ²/₃ innings last season, striking out 138 and walking 45, although his 3.95 ERA in the second half — after missing time on the disabled list with a left shoulder injury — underlined concerns about his viability.

One upside of possessing a pitching surplus in a pitching-rich market is the Mets could begin spring training with all three of their veteran starters, find assignments for them thanks to the split-squad games in the schedule and see if another team’s pitcher (or one of the Mets’ own) goes down with an injury.

Of the high-end, free-agent starting pitchers, Jon Lester looks most likely to sign first, and Lester’s decision should clear up some of the thicket as frontline starting pitchers such as Johnny Cueto of the Reds, Cole Hamels of the Phillies and Jordan Zimmermann of the Nationals are potentially available in trades. The Mets likely must wait for such options to drop in order to find optimal value for their veterans.

Among the many clubs looking for starting pitching are the Red Sox, Cubs, White Sox, Indians, Dodgers, Royals, Twins, Yankees, Pirates, Giants, Rangers and Blue Jays.