Is this a tube with as large syringe like and and a long thin rubber tube? Ie a stomach tube?
I have also heard of "lamb reviver" as a paste type mix of minerals and energy that a squirt of will give a lamb a boost.
A foster mum may well be a good option, but the ewe won't be impressed as she will know its not her lamb at this age.
You could force the issue using an adopter crate where the ewe is held by her head so she cant see or smell the lambs, usually for a few days, by which time she may accept the adoptee lamb, but still may reject it.
It may require perseverance to teach the lamb to suck a bottle, but if it is struggling, I would first check that it is not unwell, ie no temperature, clear lungs etc, your vet should be able to check the lamb and bringing it to the surgery is often an easy cheaper option for this.
How much milk are you managing to get into it? It may be being stubborn, but if its not getting enough, sometimes a boost of nutrient paste such as i described before or vitamin injection from the vet can help.
If not, you may need to top it up by stomach tube if its not getting enough. The tube is placed into the mouth, I slide it in the corner, using my finger to open the mouth and encourage the lamb to suck. Pass it gently, and you will feel the lamb chew and swallow it down and there will be no choking. Then you can give the milk down the tube. Depending on the size, a newborn triplet or native lamb will probably only have space for 50ml at a time, a big well grown single Suffolk lamb at 3 weeks would take much more. 150ml at a feed at this age is unlikely to cause any problems, but any choking you should stop immediately. The lambs stomach should feel round but not bloated when you have fed. Frequency of feeds depends how often it feels empty. I would always offer the bottle first, and it should start taking the bottle once it gets stronger.
The farmer who taught me to stomach tube lambs always said that if the tube ever goes down the wrong way into the lungs, the lamb was too weak to have survived as the throat is very well designed to swallow it down the right way.
There are also videos of how to stomach tube on youtube, sometimes easier to see it than explain!
Good luck with the little one
Suzanne