Beginning to look like CO2 would be a good bet. I see you mentioned a workshop- if you like tinkering then I would suggest either a Crosman 2250 of some sort or one of the QB78 series (which was a crosman in an earlier life )

Both are inherently very accurate (but must be 22 for better efficiency with CO2) , and both have a great parts and tune up back up. Great fun to improve them. I have one of each and they honestly are at the top end of my collection of enjoyable rifles!