Kiddyland, which occupies 3 floors in the Hankyu shopping complex in Umeda carries Tomica on their B1 floor and they are also at full retail.
Also in Umeda, on the 13th floor of the Daimaru building, one can find the newly relocated Tomica store. I believe it used to be in Namba walks a few years ago. The Tomica store, is located behind the Pokeman store and has quite a good assortment of vehicles and they have some excellent displays showcasing their products like cars, diorama buildings and train sets. They also feature a kiosk where one can have a special die-cast assembled before your eyes. All pricing here is full retail.
I later learned about a large electronics superstore called Yodobashi, in Umeda which sits on the north side of Osaka station. They carry Tomicas at the low low price of 260 yen for the regular editions. Too bad I didin't know about it when I was in Umeda.
About a 15 minute subway ride to south of Umeda, lies Namba. Just south of the Dotonbori, you can find Biccamera, the competitor to Yodobashi. They too carry Tomicas for an excellent price of 260 yen. In Namba Parks mall, a large ToysRus store has a huge inventory of Tomicas but mostly in blister packs, not so many in boxes. Their prices were 299 yen, which was lower than retail price.
A bit farther south is Nipponbashi which is also called Den Den town. This is Osaka's mecca for manga, figures and toys. There are several toy shops selling new and used die-cast, and it is here that I found Kids Land Joshin whose prices on Tomica Limited Vintage vehicles are the lowest I've seen. Their regular cars were also competitively priced at 294 yen. In some toy stores, you can also find Hot Wheels, Greenlight and even Johnny Lightning, however their prices tend towards the higher side due to lack of local interest. For example I saw mainline Hot Wheels for about 300 yen and GLs and JLs at over 800 yen each, which is quite a premium price.
If you know of any other places to find Tomica in Osaka, please let me know.