Hi Erik,
A. Do they still sell those devices?
B. Do they even sell those devices anymore?
Both sentences are grammatically correct. In sentence A, "still" is used to mean that something was done or exists in the past and continues up to the present moment. Example: The sale is still on! (The sale started some time ago and is still ongoing.) In sentence B, "even" is used to emphasise something surprising or doubtful. Example: Did he even listen to me? (You have a feeling that someone did not pay attention to you as you spoke; you would be surprised if he actually did.)
Based on these differences, sentence A asks if those devices which were sold in the past are still being sold while sentence B expresses a doubt that those devices are still being sold.
As for your other question, "anymore" implies that something that has ended or does not exist presently (e.g. To be environmentally-friendly, our supermarkets do not provide plastic bags anymore. / No one here respects the elders anymore.). You may notice that "anymore" is frequently used in forming negative sentences. (e.g. Tom doesn't live here anymore --> He used to live here but now, he doesn't.) "still" can be used with both positive and negative sentences (e.g. He still remembers the recipe. / He still cannot recall the recipe.)
Hope this helps.
Cheers