You can farm the rubies and saphires. I do believe the Hulking Stone Elementals Outside the santiarium in Ascalon drop rubies. Other critters do as well.
In all, I think the time taken to farm them might be similar to farming the cash though. I am not sure.
trade contracts 7 make one gem its better to buy 12 rubies [ and selling six and then with that money to buy your sapphs and the armor because the rubies are more valueble these days ] x
As said, just farm it, look for other quests to do, titles to work on, they will help get you the money, just dont spend anything, maybe work on protector title.
If you have more then 1 character in Nightfall, completing the quests to get the contracts from a few of your characters CAN be enough to get 1 Vabbian set for your fav character for example.
Open the free chests in NF. They have a chance to drop gems.
If you salvage things such as ruby daggers they have a chance to turn into rubies.
You fastest way is to farm for money and just buy them.
Just one more advice. It doesn't cover the way you make the money, it concerns the way you save it. As soon as you get 1K, put it in storage and don't spend it. I found i tended to spend less that way, might work for you too.
Placing a salvage inscription on Jewel Daggers and ruby mauls will still have little chance of getting rubies.
1. Do the side quest in Vabbi for the trade contracts.
2. If you have EoTN go dungeon diving and open up every hidden treasure you can find. The deeper you go the better the chance.
3. Merchant trading, do not buy rubies or sapphires from the rare material trader. You may be able to find people with rubies and sapphires in the port cities that will under-sale the rare material trader. Actually never buy from the material traders!
4. Stone Elemental can be done using a 55 Monk but still the chance for a sapphire or ruby is less than 1%. I have ran the course five times with a 55 and have only gotten 1 sapphire. Not worth the effort IMO.
5. Free chest are another way, right down when you character visits the location and wait one month before you come back.
Enjoy.
You can salvage them from geodes that drop from the beetles. I've had more luck with that than putting a salvage inscription on ruby weapons or jeweled daggers.