Sorry--I just realized I'd only read one page before posting--& there were 2 more pages of info, so I duplicated some others' comments.
More info: If you force-feed, if you feed actually down the throat (rather than just into the beak), you will need to use a 1 cc size syringe. Larger ones don't fit down the throat well.
You should be able to get needles and syringes from many people pharmacies (other than sometimes Wal-Mart, which has some kind of policy) without a problem. The needles are higher quality than a feed store's & you can get thinner needles (25-gauge is a nice thin one) and smaller syringes that are well-suited for dosing chickens. Price is about the same.
I'm wondering if your vet gave you correct dosing for the Duramycin??? LA-200 is a brand of Oxytetracycline injectible & the dose for it is 1 to 2 cc's every three days (It is a long-acting formulation), from what I know. Giving just 0.1 of Duramycin seems like too little unless it is a much more concentrated form.
I would verify the dose ASAP because it seems like they are only getting 1/10 to 1/20 of what they should!
The info at
http://durvet.com/index.php?option=com_k2&view=item&id=33:duramycin-72-200 says Duramycin 72-200 is the generic of LA-200 and they both have 200 mg Oxytetracycline per mL.
Are you using Duramycin 72-200 or Duramycin 100 injectible? Duramycin 100 is more diluted (only 100 mg Oxytetracycline per mL).
By the way, Oxytetracycline seemed very effective for my birds when they were suffering from Coryza. I hope it works well with your birds.
On the Chicken Medicine Chart, I've posted other info on Oxytetracycline that can be important for effectiveness & safety, so I'd recommend reading that, too.