Tung oil is an age old wood finishing method used by the chinese. Alot of commercial products which sell themselves as tung oil are actually wiping varnishes. Basically, thinned down lacquers.
There are similar products which go by the names Danish Oil, Antique Oil, Tru Oil, Teak Oil, Gun Stock Oil, yada yada yada...
The hardware store at Shaw is Handyman Center. It's on the same floor as the Isetan exit to the annex block. I think it's exit next to Polo Ralph Lauren. Walk out and it's on the corner on the right side. U'll pass a hair dressing saloon and a quilt store before reaching it.
Btw, u can get them at almost all DIY hardware stores.
Tung oil is a penetrating finish. It gets soaked into the wood and hardens. It's not really used like lemon oil to replenish moisture in wood, as it seals the wood if enough applications are applied.
If you're gonna use tung oil on ur guitar, I recommend using many light coats. Say around 10-15 coats, rather then putting a few thick coats on as it can get sticky and messy. Have fun.