I googled it , it says

Ok , I get it... but heres the problem

I have searched high & low in Whiterun for Amren , honestly at this point... I think I may have previously assassinated him and his corpse dissapeared

I found Athis , but he has no dialogue options for training

Then Burguk , well.... quite frankly I don't know where "The Reach" is at all , and I'm not entirely sure that a master trainer would even train anyone whos not...at a master-ish level to start off with?

What the hell? Forum so active this got knocked off of page 1 within 1 minute...

Again really? Does anyone have any answer?

Do I have to join the damn companions guild to get training from Athis?

I have a similar problem. This really svcks! Amren trained me once but once I did the quest for him he does not give me any further training options.
The one at the companions also trained me once, but once I had done all the companion quests he now does not give me a training option any longer.
The one in 'the Reach' cannot be found. I even studied the costly guide book I bought but it does not really give me an indication of where this trainer is except to say that he is in 'the reach'.

So I guess, judging by no replies to the original poster nobody knows where the one handed trainer is! This stinks!

Amren is only a journeyman trainer, so the option to train at him probably dissappears pretty fast.
You probably have to join the Companions to get training from Athis.
Dushnikh Yal is south east of Markath - http://cloud.steampowered.com/ugc/596955603805742406/60E48C2300C1F52B08EFD32460F3C95BC687DFE2/.

I already joined the companions and did all their quests and am now their 'boss' haha. But the stupid Athis does not offer me training any longer. Perhaps he begrudges my new status or something.

Amren of Whiterun, Athis of the Companions and Burguk of Dushnikh Yal in the Reach are the trainers.

One handed Skill books:
-2920, Morning Star v1 (Northwatch Keep)
-2920, Morning Star v1 (Lost Echo Cave)
-Fire and Darkness (Folgunthur)
-Fire and Darkness (Riften)
-Mace Etiquette (Orotheim)
-Mace Etiquette (Fort Greenwall)
-Night Falls on Sentinel (Swindler's Den)
-Night Falls on Sentinel (Bandit Camp: Linalta Foothills)
-The Importance of Where (Markarth)
-The Importance of Where (Chillfurrow Farm)

ah man i was planning on getting one handed training pretty soon but i erh.... kinda sacrificed Athis for something already