League of Legends (LoL) Question: Is there a ranged support that can reasonably be built as a tank?

BARD! He has great poke in lane through his meep auto-attacks and can use his Q to make plays. And the most successful Bard build is building the tanky support items. He will be eable to survive prolonged teamfights whilst aiding his team. I think he'd be a good fit for you but requires a decent amount of practice!

An unusual pick but one that actually helped me climb when I first started playing ranked:
Tank Karma. She has high base damage and shielding (with a movespeed buff), and provides utility with slows and an (unreliable) root. Building her tanky allows you to continually apply her utility spells. As you get a couple of items you become increasingly difficult to kill, and with your slows/speeds/sheilds you can normally walk away from a fight. After support item (and possibly redemption/ardent) try things like locket, frozen heart, spirit visage and even guardian angel. Make sure to hit max CDR and spam that AOE sheild for your team to soak up damage and reposition in teamfights! :)

As said above, Thresh is practically the only example of a "ranged" support that reasonably builds full tank. He's also a great support for learning a lot of stuff and has some way of playing against range with his Death Sentence.

Also any champion with a grab should be good or at least playable against mages. The other two are Nautilus and Blitzcrank. Naut is really strong top lane and you should be able to play him similarly as a support to great success.

Thresh is the first that comes to mind.

Other than that, Soraka can be built as a tank (particularly with Warmogs / Spirit Visage having decent synergy) although you aren't exactly a 'front line' tank, as your priority is still to stay in range of carries n keep them alive.

One Champion that I don't believe has been mentioned though is Annie. In lane you play as an aggressive poke support both to zone the opposing team from CS and to proc Spellthief Edge (Frostqueen claim) and pickpocket mastery (if you take it, I would personally recommend it). Mid game you want to get Frostfang, Sightstone, and then start getting tank and CDR items. At 40% CDR you can basically have your E up permanently, which when maxed gives 60 armor and MR. This also gives you a bit of choice to build some extra AP and really carry games with heavy burst and decent hard CC with your passive. Again though, you don't play as a 'front line' tank until later in the game once you get multiple tank items.

I think the only one is Thresh but it rly doesnt matter if ur range on mele if u know how to position urself in lane and in team fights.

In technicality Thresh's auto is ranged and he is a tank support. But Relic shield's execution won't work unless you last hit since he is ranged. Tank supports are having a very hard time against ranged supports but the best tank for the job in my opinion would be Braum because of his E.

There really aren't many tanky ranged supports. If you're looking for a support who can dish out a lot in teamfights, I would suggest a shielding support like Janna or Nami. My personal favorite, would be Janna. When upgraded, her shield will absorb around 250 damage and also give whoever you are shielding some extra attack damage. The best part though is when you are losing the fight, you have so much disengage.
Right now, melee supports are just getting destroyed by ranged supports it's depressing. The best supports right now, in my opinion are Lulu, Janna, Nami, Morgana or Leona.
Check out some of my guides. There's an Ivern support guide that may be of interest. He has shields and lots of cc so he can be built tanky easily. - Jurriyen Bot

You may go for a tank soraka, although you'll need to go for the ardent censer compensate for lesser healings from your abilities.

i think it will get a late game in 45 minutes.
but sometimes it is be good in the player to build what upon on his climb.