There are lot's of places online to buy scottish stuff.. Mostly over priced and aimed at tourists.. What I (I'm Scottish by the way) usually do is use these sites for ideas and then buy the same stuff cheaper on ebay :)

Somebody who's 50 probably has everything eh.. What about something personalised, like a hip flask or sgian dubh (various spelling of that) ? Does he have a tartan - or one that could be loosley associated? 

Find a tartan:

http://www.tartans.scotland.net/find_tartan.cfm.htm

Check some gifty things

http://www.thecelticshop.co.uk/pewter_hip_flasks.htm

Some scottish food: (you should also add some Irn Bru)

http://www.scottishfoodoverseas.com

Or maybe just get nice wiskey - everybody loves that - no? Can even get the name on it.

http://www.masterofmalt.com/personalised-whisky/

I'm not Scottish but I've been there recently on a holiday.

Some ideas: 

1. Whisky. Should be #1. 

2. Angus Beef (not sure where you can get that)

3. As John mentioned - a tartan. 

4. Sticky Toffee Pudding (easy to make yourself, and incredibily tasty)

5. Anything to protect your uncle from the rain

6. Something to do in Scotland while it's raining (e.g. games, reading)

7. Scottish literature, e.g. Walter Scott

8. Scottish movies, e.g. Trainspotting, Braveheart, Stone of Destiny. 

9. Does he hike? A book with hiking trails or hiking equipment. 

Get him a Quaich - it is a "sharing cup" ... my friend recently gave me one, with a personal message enscribed on it, for being an Usher at his wedding - very nice, personal gift.

Like John, above, I do the same thing... a quaich should cost around £30 (45 chf)..  

Hi there

I am Scottish and make Scottish gifts but maybe not quite suitable for a man....they are called 'a wee mindin' which is a Scottish term meaning a small gift to remind you of me.  They are tartan hanging hearts with a metal stags head sewn on the front.  The box can also be personalised to suit.  See pic for example.

I also make cushions that can also be personalised, I've attached pics for you. If you are in a rush I'm not sure what tartan/tweed fabric I have for the cushion as I'm just about to re-order.

Whisky is definitely a good one and a personalised quaich a nice touch.  Or you could organise a whisky visit for wherever he is in Scotland when he is on his travels.  If he is in Edinburgh there is a great whisky experience:

http://www.scotchwhiskyexperience.co.uk/

Hope this helps, best of luck,

Suz