I'll put in another vote for a tailor, and if you want to get geeky about suits and their quality/fabrics, check out styleforum. I don't think there's a group out there that knows more about suits than they do. I selected an older suit, had it tailored and was complimented as one of the best dressed at a recent wedding I went to. I scored a few nice looking high end ties and dress shirts on ebay for cheap. Generally I'll conceal OWB with a Raven Concealment holster, glock 19, PHLster flat pack + TQ. Not as much gear as the OP, but tailors help with that stuff.
As a guy who has been blessed to not have to do the suit or tux thing often, I have had great luck with Men’s Wearhouse with the right sales guy at the locations I have used. I was fitted with all my guns and equipment with nobody freaking out. They did reinforced larger belt loops and have a lot of locations if you need an emergency fix or alteration. I HAVE to be custom fit for everything. They have been the by far the best of the non custom bespoke world to deal with in my experience. The biggest plus was non-judge mental and no negative attitude at all and actually wanted to help. This was not what I found elsewhere.
You are right in my wheel-house after 16+ years of dress-suit-based EP work... Best option, as jcustisredux states, is custom tailor from the start.
You can do Mens Whorehouse or Jose`Banks, but I've found those suits tend to: a) wear out as fast as anything due to your gear and likely activity level, b) end up costing you just as much as custom when you factor in the alterations you need, and c) due to the likely alterations you very possibly end up looking like a soup sandwich in your big brother's suit. If you just need 1 or 2 suits for the urgent and/or occasional gig and you're an easy/off-the-rack fit, they are certainly an adequate solution, but if you're going to be dressed like this 40+ hrs/week (and particularly if your clientele is high profile and you're going to find yourself inadvertently photographed....), you'll be thankful you did it right by going custom.
There are some custom tailors that do alot of work for EP, cops, DSS, and USSS types. One that I've used with good results is Hong Kong based, but does a traveling roadshow around the US 2-3x per year, doing sizing and fitting by appointment, then ships you your items a few weeks later. He's got a full palate of colors, fabrics, price points, etc. and does shirts also (Note I HATE the fit of off-the rack shirts, way too baggy...) Its not uncommon to walk into an appointment with him and see guys doing a fitting in full belt/kit and low-viz armor, and they'll be simulating a shooting stance/sitting/squatting (crotch tightness is problem with the trend toward tighter European-cut suits...), and then getting into the finer points of size, quantity, and placement of pockets and belt loops. You'll want to do same if you want anything to fit right while actually working. I know he's coming for another round in July-Aug. PM me for details.
Lastly - There's also the http://www.coolactionsuitDOTcom supposedly designed with input from USSS/DSS types, but I dont know anyone personally who has one who can offer review. I'm wary of buying a suit off the internet without a proper tailor, but I'm hard to fit anyway..... YMMV.
Are you talking about Fitwell? If so, I've had great luck with them and their prices are reasonable for custom made suit, too.
Best shirts I've found to date, made in America, in Texas: https://hamiltonshirts.com/
Preach it Doc, been wearing Hamilton shirts w/ suits ‘n sport coats since ‘96 & made in H town to boot.
Men's Wearhouse has been very solid over the years.