well. The most expensive way of getting them is, of course, buying them. Like Grumdor said, there are two ways to get the pots.
The fastest way is by using sealstones.
In the week where one side has won, you can go to the priest of the winning side and exchange your sealstones for ancient adena (aa). At the priest you can then exchange your aa for these pots. The priests charges the following.
Greater haste potion cost 3600aa + 240a
Greater swift attack potion cost 7200aa + 480a
Greater magic haste potion cost 7200aa + 480a
If you rather want to fish for them you need to have learned common craft lvl 3. Common craft levels are learned automatically when you level, but dont remember exact level you have to be to get lvl 3. Ill check it for you and add it to the post. Then you will need the recipees. Easiest way is just buying them. On my server they go for 50k.
then you need to fish 8) . The recipees are as follows:
Greater swift attack potion : 10 greater fish oil & 12 fish scale
Greater magic haste potion : 10 greater fish oil & 12 fish scale
Greater haste potion : 4 greater fish oil & 7 fish scales
One thing to note about fishing is that you need to be certain levels to get the different obtainable items. The best level of fishing skills for these items are around level 10, as the fish that give the most of these items are found at this level.
Finally, you will probably get a recipe for greater fish oils, while fishing. Register it and convert normal fish oils while doing your fishing. 4 fish oil convert to 1 greater fish oil if I remember correctly.