1A fuse instead of 1/2A fuse: any problem?

If you need to deviate you want something that will blow sooner rather than later. A 1A fuse won't blow as soon as a 0.5 amp fuse. It will tolerate a higher "spike" that might damage your equipment. Replace fuses as recommended by the OEM or with a lower amp rated fuse if you must deviate.

Ezekiel makes a good point about "fast blow" vs "slow blow". I did need to replace a fuse at one point and Radio Shack did have them.

Sorry - I lost track of your original issue. HiFi Tuning Fuses from the Cable Company might be an option. They appear to have an 0.5 amp option in 2 different size fuses. I used a Radio Shack fuse temporarily and then switched to one of these for my power amp. I thought I heard an improvement in sound.

See the link below. Click on the order form and scroll way down to see the list of amp ratings & sizes etc.
http://www.fatwyre.com/featuredprods.html