Happy new year to all.
I have Sora group set on my drop bar bike
(FD-RD-ST 3000)
I decide to convert it to flat bar, I found the SL-3000 in a bike shop on my neighbourhood but I can't find the Sora brake levers (R3000) there. Can I use the Alivio T4000 brake levers with Sora flat bar shifters? Or is there any conflict with the shapes of those shifters? I notice that the Sora seems more curvy than Alivio. Do they match well?
Thank you.

If you are running short pull brakes like road caliper brakes you need a lever designed for them. In the end there are tons of hybrids out there and hybrids generally have more tire clearance so I would just advise someone to get a better hybrid instead and either use this bike as a beater or sell it.

Of course you are not going to find it sitting on the shelf in your local bike shop. Just buy it online:
https://www.ebay.com/itm/116069702423

Of course you won't find brake levers at the bike shop? Good one! You also won't find authorized dealers on ebay for Shimano.

Your local bike shop has a very limited floor space. Of course they are not going to stock the entire Shimano line-up. Why is that surprising?
And it's a $25 pair of brake levers. You don't have to buy from an 'authorized dealer'.

Any flat bar levers designed for short pull brakes will work fine.

So buy a new bike instead of a couple levers for around $50 to finish their handlebar change????
FWIW I checked with my LBS (that has 10 locations) and L&R BL-R3000 I can have in 10 days so really no different than buying online

Correct but no need to mention the bike shop then you could just made your buy it from a random seller comment without denigrating bike shops.
The cost of the item has nothing to do with anything. Buying from an authorized dealer ensures if you actually have a problem you get support from in this case Shimano. It may not be needed but I would rather have to pay $25 for the levers and then get them warrantied if there is a problem rather than spending $50 for two levers.

dedhed A road bike generally has poor tire clearance so while you can get a little more upright the comfort is not going to be able to improve greatly but wider tires help a huge amount. It was not a value proposition it was about getting someone more comfortable.

The Shimano road flat bar levers have a flip chip so they can work with any kind of cable brake. There are Claris, Sora, and Tiagra versions but the only obvious difference is the paint. There's one version with a forged aluminum rather than stamped steel lever. You can tell by the ball on the end. A bike shop shouldn't be expected to stock these, as they are a weird conversion part. 99% of bikes with flat bar cable brakes are long-pull. They need all their floor and storage space for bikes and clothes that make them money. Most bike shop work is consumables, adjustments, and bending things back.

The OP never mentioned comfort or bigger tires as a reason to go with flat bars. It may be as simple as back issues or just wants to sit upright.
FWIW my hybrid has 25's on it as I almost exclusively use it on roads and paved trails, the original 32's were extremely noisy, and I had 25's in stock.

No but having done a few of these conversions for people over the years they will usually come back and say I am still not where I want to be and they want wider tires. Not everyone but a lot of people don't understand wider tires and are stuck in the olden days where speed isn't speed unless you feel it (which is actually slower but...).